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Introduction: The bortezomib, lenalidomide, and dexamethasone (VRd) regimen is an acceptable standard of care (SoC) for both transplant-eligible and transplant-ineligible newly diagnosed multiple myeloma (TI NDMM). Ongoing development of novel therapies and combinations strive to improve survival outcomes beyond what is expected from SoC. Belantamab mafodotin (belamaf) is a B-cell maturation antigen-binding antibody-drug conjugate that eliminates myeloma cells by a multimodal mechanism and has demonstrated durable responses in patients with relapsed/refractory multiple myeloma (RRMM). Preclinical evidence of belamaf in combination with bortezomib or lenalidomide suggests enhanced anti-myeloma activity, providing rationale for this treatment combination. We report the preliminary findings of belamaf + VRd for TI NDMM patients. Methods: DREAMM-9 (NCT04091126) is an ongoing Phase I, open-label, randomized, dose and schedule evaluation study of belamaf + VRd in patients with TI NDMM. Eligible patients include those ≥18 years old with ECOG status 0-2 and adequate organ system functions. The study evaluates safety and tolerability of belamaf + VRd in up to 8 cohorts, up to 144 patients, to establish the recommended phase 3 dose (RP3D). VRd is administered Q3W until cycle 8, followed by lenalidomide + dexamethasone (Rd) Q4W. Belamaf + VRd is administered until cycle 8, and then in combination with Rd thereafter. The belamaf dose cohorts currently being evaluated are: cohort 1 (1.9 mg/kg Q3/4W), cohort 2 (1.4 mg/kg Q6/8W), cohort 3 (1.9 mg/kg Q6/8W), cohort 4 (1.0 mg/kg Q3/4W), and cohort 5 (1.4 mg/kg Q3/4W). After evaluation of safety data for cohort 1, cohorts 2-5 were opened in parallel and enrolled patients were randomized 1:1:1:1. Safety data, clinical activity, and drug concentrations will be assessed, and used to determine the belamaf RP3D. This analysis reports the preliminary results from cohort 1. Primary endpoints include number of patients with adverse events (AEs). Secondary endpoints include establishing relative dose intensity of lenalidomide and bortezomib in combination with belamaf, cumulative dose of belamaf, pharmacokinetics (PK) profile of belamaf when combined with VRd, overall response rate (ORR), complete response (CR), stringent complete response (sCR), complete response rate ([CRR]; % of patients with a confirmed CR or better), and rate of very good partial response or better (≥VGPR). Exploratory endpoints include assessing minimal residual disease (MRD) in patients who achieve ≥VGPR, and safety and efficacy exposure-response relationships. Results: Twelve patients in cohort 1 were included in this preliminary analysis. Eight patients (67%) were male; median age (range) was 72.5 years (63-77). Ten patients (83%) were white and 2 (17%) were Asian. Nine patients (75%), were ISS stage II or III, and 4 (33%) patients had high-risk cytogenetics (consisting of one or more of the following: t(4;14), t(14;16), del17p, 17p13del). AEs related to study treatment were experienced by all 12 patients. Dose reductions occurred in 12 (100%) patients, all of whom also experienced a dose delay. Most common AEs leading to dose modification were thrombocytopenia, neutropenia, and corneal events. Grade 3 or 4 AEs related to belamaf occurred in 9 (75%) patients. During the trial, one patient experienced a fatal severe AE due to COVID-19 infection (unrelated to study treatment; Table). All patients, 100% (n=12; 95% CI: 73.5-100) achieved ≥VGPR. Early deep responses were observed; 2 (17%) patients achieved VGPR as early as 4 weeks. As of data cut-off, 5 (42%) remain in CR and 3 (25%) in sCR. Based on real-time data captured in the clinical database, 7 out of 9 patients achieved MRD-negative status at the first test after VGPR. Belamaf PK profile was similar to that observed in patients with RRMM taking into consideration baseline patients characteristics. Conclusion: Preliminary data suggest addition of belamaf to VRd did not reveal new safety signals and demonstrates high response rates, albeit with short follow-up. The study is ongoing to confirm safety and evaluate the efficacy of belamaf + VRd. Updated data for cohort 1 will be reported at the congress. Funding: GSK (Study 209664); belamaf drug linker technology licensed from Seagen; belamaf monoclonal antibody produced using POTELLIGENT Technology licensed from BioWa. Figure 1 Figure 1. Disclosures Usmani: Pharmacyclics: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Takeda: Consultancy, Research Funding, Speakers Bureau; Merck: Consultancy, Research Funding; SkylineDX: Consultancy, Research Funding; Sanofi: Consultancy, Research Funding, Speakers Bureau; Janssen: Consultancy, Research Funding, Speakers Bureau; Janssen Oncology: Consultancy, Research Funding; Bristol-Myers Squibb: Research Funding; EdoPharma: Consultancy; GSK: Consultancy, Research Funding; Celgene/BMS: Consultancy, Research Funding, Speakers Bureau; Array BioPharma: Consultancy, Research Funding; Abbvie: Consultancy; Amgen: Consultancy, Research Funding, Speakers Bureau. Quach: Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; GlaxoSmithKline: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen/Cilag: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Antengene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; CSL: Consultancy, Membership on an entity's Board of Directors or advisory committees. Koh: Pfizer: Consultancy; Jassen: Honoraria; AstraZeneca: Honoraria; Novartis: Honoraria; GSK: Honoraria; Roche: Honoraria; Takeda: Honoraria. Guenther: Novartis: Consultancy; Celgene: Consultancy, Honoraria; Roche: Consultancy; Takeda: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; AbbVie: Consultancy; Jazz Pharmaceuticals: Honoraria; Janssen Pharmaceuticals: Consultancy, Honoraria. Zhou: GlaxoSmithKline: Current Employment. Kaisermann: GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Mis: GlaxoSmithKline: Current Employment. Williams: GlaxoSmithKline: Current Employment. Yeakey: GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Ferron-Brady: GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Figueroa: GlaxoSmithKline: Current Employment. Kremer: GlaxoSmithKline: Current Employment. Gupta: Novartis: Current equity holder in publicly-traded company; GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Janowski: Celgene: Consultancy; AstraZeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees.

Introduction: Belantamab mafodotin (belamaf; GSK2857916) is a B-cell maturation antigen (BCMA)-targeting antibody-drug conjugate. In the pivotal Phase II DREAMM-2 study, single-agent belamaf demonstrated deep and durable responses and a manageable safety profile in patients refractory and/or intolerant to ≥3 lines of therapy, including an anti-CD38 monoclonal antibody such as daratumumab (Lonial et al. Lancet Oncol 2020). Responses were sustained at 13 months of follow-up with belamaf (2.5 mg/kg intravenously [IV] every 3 weeks [Q3W]); overall response rate (ORR) was 32% and median duration of response (DoR) was 11.0 months (Lonial et al. ASCO 2020 Poster 436). Triple combination regimens, such as daratumumab plus bortezomib and dexamethasone (D-Vd), are considered a standard of care for patients with RRMM and have demonstrated superior antimyeloma activity to monotherapy and dual combination regimens, such as bortezomib and dexamethasone. Preclinical data suggest synergistic antimyeloma activity of belamaf and bortezomib (a proteasome inhibitor), and initial results from the ongoing Phase I/II DREAMM-6 study of B-Vd indicate an acceptable safety profile for the combination (Nooka et al. ASCO 2020 Oral 8502). The DREAMM-7 study (NCT04246047) will evaluate the efficacy and safety of B-Vd compared with D-Vd in patients with RRMM. Methods: DREAMM-7 is an ongoing, randomized, open-label, global, multicenter, Phase III, two-arm study in patients with measurable RRMM who had received ≥1 prior therapy with documented disease progression during or after their most recent therapy. Patients aged ≥18 years with Eastern Cooperative Oncology Group Performance Status 0-2, adequate organ system function, and who provide informed consent will be eligible. Patients intolerant/refractory to daratumumab or bortezomib, or with prior exposure to anti-BCMA therapy, will be excluded. Patients will be stratified by the Revised International Staging System, prior exposure to bortezomib, and number of prior lines of therapy. Approximately 478 patients will be randomized (1:1) to Arm A (B-Vd) or Arm B (D-Vd). In Arm A, patients will receive belamaf 2.5 mg/kg (IV) Q3W on Day 1 of each cycle; bortezomib 1.3 mg/m2 (subcutaneously) on Days 1, 4, 8, and 11 of Cycles 1-8 (21-day cycles); and dexamethasone 20 mg (IV or orally) on the day of, and the day after, bortezomib treatment. In Arm B, patients will receive daratumumab 16 mg/kg (IV) in 21-day cycles: Cycles 1-3 Q1W, Cycles 4-8 Q3W, and from Cycle 9 onwards Q4W; dexamethasone and bortezomib schedules will be the same as in Arm A. Treatment will continue in both arms until disease progression, death, unacceptable toxicity, withdrawal of consent, or study end. The primary endpoint is progression-free survival (PFS; time from randomization to the earliest date of documented disease progression or death [any cause]). The key secondary endpoint is minimal residual disease negativity rate, as assessed by next-generation sequencing. Additional secondary endpoints include complete response rate, ORR, DoR, PFS2 (PFS after initiation of new anticancer therapy), overall survival, and endpoints related to pharmacokinetics, antidrug antibodies, safety, and health-related quality of life. As of August 2020, the study is enrolling. Funding: GSK (Study 207503); drug linker technology licensed from Seattle Genetics; mAb produced using POTELLIGENT Technology licensed from BioWa. Disclosures Rifkin: McKesson: Current equity holder in publicly-traded company, Ended employment in the past 24 months, Other: Stock ownership; Takeda, Amgen, Celgene, BMS, Mylan, Coherus BioSciences, Fresenius: Consultancy; AbbVie: Other: Investigator in AbbVie sponsored clinical trials; Takeda, Amgen, BMS (Celgene): Membership on an entity's Board of Directors or advisory committees. Boyd:Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Takeda: Consultancy, Honoraria. Di Raimondo:Amgen: Consultancy, Honoraria; GILEAD, Incyte: Research Funding; Amgen, Takeda, Novartis: Honoraria; Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; GSK: Consultancy, Honoraria; Takeda: Consultancy, Honoraria. Dimopoulos:Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees, Research Funding, Speakers Bureau; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees. Weisel:Janssen: Consultancy, Honoraria, Research Funding; Sanofi: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria; Adaptive: Consultancy, Honoraria; GlaxoSmithKline: Honoraria; Karyopharm: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria. Arnulf:BMS: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Celgene: Research Funding; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria. Hajek:Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding; Pharma MAR: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Oncopeptides: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding. Spencer:AbbVie, Celgene, Haemalogix, Janssen, Sanofi, SecuraBio, Specialised Therapeutics Australia, Servier and Takeda: Consultancy; Amgen, Celgene, Haemalogix, Janssen, Servier and Takeda: Research Funding; AbbVie, Amgen, Celgene, Haemalogix, Janssen, Sanofi, SecuraBio, Specialised Therapeutics Australia, Servier and Takeda: Honoraria; Celgene, Janssen and Takeda: Speakers Bureau. Davis:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Riccio:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Kim:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Wilkes:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Rutledge:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Talekar:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Kremer:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Gupta:Novartis: Current equity holder in publicly-traded company; GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Mateos:Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie/Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; PharmaMar-Zeltia: Consultancy; Regeneron: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen-Cilag: Consultancy, Honoraria; GlaxoSmithKline: Consultancy; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction: The treatment paradigm for RRMM is characterized by continuous treatment to suppress the malignant plasma cell clone. Some treatments may affect the eye, leading to a broad spectrum of ocular disorders, from dry eye to glaucoma, causing impaired quality of life. Therefore, we examined the baseline eye health of patients with RRMM receiving single-agent belamaf in the DREAMM-2 study (NCT03525678) and compared the findings to those of age-matched individuals in the general population. A better understanding of baseline ocular status is important as patients may have existing, undiagnosed eye conditions that may affect future treatment options. Methods: DREAMM-2 investigated belamaf, a B-cell maturation antigen-targeted antibody-drug conjugate in patients with RRMM. Eligible patients had received ≥3 prior therapies and were refractory to an immunomodulatory agent, a proteasome inhibitor, and refractory and/or intolerant to an anti-CD38 monoclonal antibody. Prior to receiving belamaf, patients underwent systematic ocular history collection and eye examination and completed the eye-specific National Eye Institute Visual Function Questionnaire 25 (NEI-VFQ-25). We report pretreatment eye-related findings to describe the baseline ocular status of patients with RRMM in DREAMM-2. Results: Of 221 patients enrolled, 100 (45%) were female and 121 (55%) were male, with a median age (range) of 66 years (34-89), median time from diagnosis of 5.4 years (1.1-12.1), and median 6 (3-21) prior lines of therapy; 98% patients had received bortezomib. Previous ocular history reported by patients were cataract (60%), intraocular surgery and/or laser treatment (35%), dry eye (20%), and glaucoma (6%), and history of ocular disease requiring medical treatment (12%). On examination, the mean best corrected visual acuity (BCVA) Snellen score was worse than 20/50 in one or both eyes in 20 and 4 of 218 patients with data, respectively. Blepharitis (anterior) was evident in approximately 20% and the corneal epithelium was abnormal (mainly mild-grade keratopathy) in 43% of patients. Impaired tear film production was reported with meibomian gland dysfunction (MGD) in 33% of patients, and evidence of dry eye (Schirmer's test, median 8.2 mm [normal ≥15 mm] in the worse eye. Median worse-eye tear break up time was 8.6 sec [normal >10 sec]). Slit-lamp examination revealed a cataract in approximately 50% of patients. Ten (8%) patients had evidence of prior cataract surgery with an implanted lens (pseudophakia). Dilated fundoscopy identified an abnormal optic nerve in 10% of patients in either eye; of these, glaucomatous cupping was noted in 43% (right eye) to 50% (left eye) of patients. Median (range) overall composite vision score by NEI-VFQ-25 was 95.3 (28-100). Conclusions: There was a 60% prevalence of cataract in the study cohort and an increased prevalence of glaucoma (6% vs expected 3% in patients >65 years old; Kreft et.al. BMC Public Health 2019) in RRMM patients treated in the DREAMM-2 study. Both conditions can be associated with corticosteroids, often used in MM treatments, although cataract is also an age-related phenomenon. We noted a significant number of patients with blepharitis (anterior), dry eye, and MGD, which may be associated with prior bortezomib treatment. Forty-three percent of patients had an abnormal corneal epithelium at baseline, which may be related to dry eye. This is relevant as belamaf is associated with keratopathy (microcyst-like epithelial changes visible on slit-lamp examination, with or without symptoms). Overall NEI-VFQ-25 scores were comparable to those reported in patients >65 years old (Nickels et al. Health Qual Life Outcomes 2017). Patients with RRMM may have a number of baseline ocular abnormalities suggesting a need for regular ophthalmic examinations in this vulnerable population to identify and manage underlying conditions and treatment-related complications. Specifically, attention should be paid to patients who may have ocular conditions associated with prior treatment with corticosteroids or bortezomib. The optimization of ocular heath in this population is particularly relevant given that emerging RRMM therapies such as belamaf are associated with significant ocular side effects. Funding: GSK (Study 205678); drug linker technology licensed from Seattle Genetics; monoclonal antibody produced using POTELLIGENT Technology licensed from BioWa. Disclosures Popat: GSK: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Celgene: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Other: Travel support, Research Funding; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); AbbVie: Consultancy, Honoraria. Farooq:University of Chicago: Current Employment; GlaxoSmithKline: Consultancy. Thulasi:Emory University: Current Employment. Lonial:Novartis: Consultancy, Honoraria, Other: Personal fees; Janssen: Consultancy, Honoraria, Other: Personal fees, Research Funding; BMS: Consultancy, Honoraria, Other: Personal fees, Research Funding; GSK: Consultancy, Honoraria, Other: Personal fees; Abbvie: Consultancy; Merck: Consultancy, Honoraria, Other: Personal fees; Takeda: Consultancy, Other: Personal fees, Research Funding; Amgen: Consultancy, Honoraria, Other: Personal fees; Sanofi: Consultancy; Genentech: Consultancy; Karyopharm: Consultancy; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees; JUNO Therapeutics: Consultancy; Millennium: Consultancy, Honoraria; Onyx: Honoraria. Jakubowiak:AbbVie, Amgen, BMS/Celgene, GSK, Janssen, Karyopharm: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive, Juno: Consultancy, Honoraria. Badros:Amgen: Consultancy; University of Maryland: Current Employment. Jeng:University of Maryland: Current Employment; EyeGate: Current equity holder in publicly-traded company; Kedrion, Merck, GSK: Consultancy. Opalinska:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Baron:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Piontek:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Byrne:Adaptimmune, Novartis: Current equity holder in publicly-traded company; GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Womersley:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Gupta:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company; Novartis: Current equity holder in publicly-traded company. Degli Esposti:Moorfields Eye Hospital: Current Employment; GlaxoSmithKline: Consultancy, Honoraria.

Introduction: IRRs are commonly reported by patients receiving intravenous (IV) treatments for RRMM (Nooka et al. J Oncol Pract 2018); these can be troublesome for patients and can lead to discontinuation of treatment, negatively impacting durability of response. In the Phase II DREAMM-2 study (NCT03525678), single-agent belamaf (GSK2857916), a first-in-class B-cell maturation antigen (BCMA)-targeting antibody-drug conjugate, demonstrated deep and durable responses with a manageable safety profile in patients with heavily pre-treated RRMM (Lonial et al. ASCO 2020; poster 436). As expected with IV biologic agents, IRRs were commonly reported in this study, but were considered self-limited. Here, we report details on IRRs for patients receiving belamaf 2.5 mg/kg (the recommended dose for future clinical development) after 13-months of follow-up. Methods: In the DREAMM-2 study, patients with RRMM progressing after ≥3 prior therapies, refractory to an immunomodulatory agent and a proteasome inhibitor, and refractory and/or intolerant to an anti-CD38 monoclonal antibody, and who provided informed consent, received single-agent belamaf (2.5 or 3.4 mg/kg IV every 3 weeks) on Day 1 of each cycle until disease progression or unacceptable toxicity. Pre-medication for IRR prophylaxis was not protocol mandated (administered per investigator discretion, if deemed medically appropriate). These events were graded by Common Terminology Criteria for Adverse Events criteria version 4.03 and included the terms: IRR, pyrexia, chills, diarrhea, nausea, asthenia, hypertension, hypotension, lethargy, and tachycardia. Grade 2 IRRs were managed by stopping the infusion, providing medical treatment and continuing the infusion at half the original infusion rate until resolution to Grade ≤1. Grade 3 IRRs were managed by discontinuing the infusion until recovery to Grade ≤1, after which the treatment could only continue (with pre-medication and a longer infusion time) following discussion with the study sponsor; all future infusions were pre-medicated. Patients experiencing Grade 4 IRRs were permanently withdrawn from the study. IRRs were followed until resolution/stabilization. Results: After 13-months of follow-up, IRRs occurred in 20/95 (21%) patients; most were mild to moderate in severity, with no Grade 4 or 5 events (Grade 1, n=6 [30%]; Grade 2, n=11 [55%]; Grade 3, n=3 [15%]). Pyrexia was reported in 5/20 (25%) patients; chills, diarrhea, and nausea in 2/20 (10%) each; asthenia, hypertension, lethargy, and tachycardia in 1/20 (5%) patients each; and the adverse event term 'IRR' was recorded for 16/20 (80%) patients. In most patients (18/20 [90%]), IRRs occurred during Cycle 1, and the incidence of these events declined thereafter (Figure). Of 73/95 (77%) patients without pre-medication at Cycle 1, 12 (16%) experienced an IRR. A total of 22/95 (23%) patients received a pre-medication at Cycle 1; of these, 8 (36%) had an IRR. Among the 20 patients experiencing an IRR, 11 (55%) received ≥1 pre-medication over the course of the study (most commonly: antihistamine, n=6 [30%]; analgesic (paracetamol); n=7 [35%]; steroid, n=6 [30%]). The median time of onset of the first IRR occurrence was at Day 1 (range: 1-22). The median duration of IRRs was 1 day (range: 1-3). Most patients experiencing IRRs (12/20 [60%]) had only one event; 3 (15%) experienced two IRRs and 5 (25%) patients had ≥3 events. Treatment was permanently discontinued due to IRRs in 1 (5%) patient (Grade 3 IRR at first and second infusion); no dose reductions or interruptions/delays occurred due to an IRR. At 13-month follow-up, IRRs were considered recovered/resolved in most (18/20 [90%]) patients (recovered/resolved with sequelae; recovering/resolving, n=1 [5%] each). Conclusions: As expected with biologic treatments administered via IV infusion, IRRs were reported with belamaf in the DREAMM-2 study. However, IRRs were typically mild-to-moderate in severity and most were considered resolved at 13-month follow-up. Importantly, IRRs resulted in few dose modifications or discontinuations, allowing patients to continue active belamaf treatment, which has been associated with durable responses in patients with RRMM. Funding: GSK (Study 205678; drug linker technology licensed from Seattle Genetics; monoclonal antibody produced using POTELLIGENT Technology licensed from BioWa. Disclosures Nooka: Karyopharm Therapeutics, Adaptive technologies: Consultancy, Honoraria, Research Funding; Spectrum Pharmaceuticals: Consultancy; Adaptive Technologies: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria, Other: Personal Fees: Travel/accomodations/expenses, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Sanofi: Consultancy, Honoraria; Oncopeptides: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding. Lee:Celgene: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Genentech: Consultancy; Takeda: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Sanofi: Consultancy; Daiichi Sankyo: Research Funding; Regeneron: Research Funding; Genentech: Consultancy; GlaxoSmithKline: Consultancy, Research Funding. Badros:Amgen: Consultancy; University of Maryland: Current Employment. Voorhees:TeneBio: Honoraria, Other: Other relationship; Janssen: Honoraria, Other: Other relationship; Adaptive Biotechnologies: Honoraria, Other: Other relationship; Oncopeptides: Honoraria, Other: Other relationship; Novartis: Honoraria, Other: Other relationship; GSK: Honoraria, Other: Other relationship; BMS/Celgene: Honoraria, Other: Other relationship. Hultcrantz:Intellisphere LLC: Consultancy; Amgen: Research Funding; Daiichi Sankyo: Research Funding; GSK: Research Funding. Karlin:Sanofi: Honoraria; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, personal fees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, personal fees; Celgene/Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, personal fees; Celgene: Other: Personal fees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees. Arnulf:BMS: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy, Honoraria; Celgene: Research Funding. Richardson:Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. Zhi:GSK: Current Employment, Current equity holder in publicly-traded company. Baron:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Piontek:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Lewis:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Opalinska:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Gupta:Novartis: Current equity holder in publicly-traded company; GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Cohen:Novartis: Other: Patents/Intellectual property licensed, Research Funding; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Takeda,: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Kite Pharma: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Genentech/Roche: Membership on an entity's Board of Directors or advisory committees. Lonial:Karyopharm: Consultancy; Sanofi: Consultancy; Amgen: Consultancy, Honoraria, Other: Personal fees; Takeda: Consultancy, Other: Personal fees, Research Funding; Novartis: Consultancy, Honoraria, Other: Personal fees; Janssen: Consultancy, Honoraria, Other: Personal fees, Research Funding; BMS: Consultancy, Honoraria, Other: Personal fees, Research Funding; GSK: Consultancy, Honoraria, Other: Personal fees; Abbvie: Consultancy; Merck: Consultancy, Honoraria, Other: Personal fees; JUNO Therapeutics: Consultancy; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees; Millennium: Consultancy, Honoraria; Genentech: Consultancy; Onyx: Honoraria.

Introduction: Patients with heavily pretreated RRMM have a poor prognosis (median overall survival [OS]: 6-9 months) and a need for novel, well-tolerated treatments that induce lasting responses (Gandhi Leukemia 2019; Chari NEJM 2019). Belamaf (GSK2857916) is a first-in-class, B-cell maturation antigen-targeting, antibody-drug conjugate (ADC) containing monomethyl auristatin F (MMAF). In DREAMM-2 (NCT03525678), patients with heavily pretreated RRMM who responded to single-agent belamaf maintained deep and durable responses at 13-month follow-up (median OS: >13 months) with a manageable safety profile (Lonial ASCO 2020, Poster 436). Consistent with other MMAF-containing ADCs, ocular events were common (Farooq et al. Ophthal Ther 2020). These events included keratopathy (microcyst-like epithelial changes [MECs]: an eye exam finding with/without symptoms), best-corrected visual acuity (BCVA) changes, and symptoms (blurred vision and dry eye). Longer-term recovery data will help inform management strategies. Methods: In DREAMM-2, eye exams were conducted at baseline and prior to each dose in patients received single-agent belamaf (2.5 or 3.4 mg/kg Q3W) and included a corneal exam and assessment of BCVA change from baseline (Snellen visual acuity [VA]). Dose modifications (delays/reductions) were permitted to manage these events. The corneal events were graded per the Keratopathy and Visual Acuity (KVA) scale, which combined corneal exam findings and BCVA changes from baseline. Dose modifications were determined based on the most severe KVA scale grade. These events were followed until recovery, defined as any Grade 1 exam findings/no exam findings, and ≤1-line decline in Snellen VA compared with baseline. A change to a BCVA 20/50 or worse (ie, limiting driving ability) in the better-seeing eye (in patients with BCVA better than 20/50 at baseline) was considered one definition of clinically meaningful VA decrease. Recovery of these events was defined as BCVA improvement to better than 20/50 (better-seeing eye). We report ocular event outcomes for patients receiving belamaf 2.5 mg/kg (recommended dose for future clinical development) from a 13-month follow-up post-hoc analysis. Results: In patients receiving single-agent belamaf 2.5 mg/kg, 72% (68/95) experienced a treatment-related eye exam finding of keratopathy (MECs) (Farooq Ophthal Ther 2020).Fewer patients (56%; 53/95) had symptoms (eg, blurred vision or dry eye) and/or a ≥2-line BCVA decline (better-seeing eye). Treatment discontinuations due to ocular events were rare (3% [3/95] total; 1% [1/95] each due to keratopathy [MECs], blurred vision, and reduced BCVA (Farooq Ophthal Ther 2020). In patients with keratopathy (MEC) events Grade ≥2 per KVA, 48% (29/60) had >1 event. The first event recovered in 77% (46/60; Table; Farooq Ophthal Ther 2020). At last follow-up, 48% (29/60) had documented recovery of their most recent event (Farooq Ophthal Ther 2020). In patients with unrecovered events at last follow-up, 45% (14/31) are receiving treatment or in follow-up. The remaining 55% (17/31) are no longer in follow-up (9 died; 4 withdrew from study; 4 lost to follow-up). 84% (37/44) of patients with Grade 3/4 events were improving or had recovered events at last follow-up. Seventeen (18%) patients had a clinically meaningful BCVA decline, with no reports of complete permanent vision loss (Farooq Ophthal Ther 2020). Of these patients, 76% (13/17) had 1 event and 24% (4/17) had 2 events (no patients had >2 events). 82% (14/17) had recovery of their first event and 82% (14/17) had recovery at last follow-up (Farooq Ophthal Ther 2020). Of the remaining 3 patients with unrecovered events, 1 patient is receiving treatment and 2 patients are no longer in follow-up (1 died due to disease progression; 1 withdrew from study). Conclusions: Though keratopathy (MECs) were frequently observed on eye exam, the majority of patients did not experience a clinically meaningful BCVA decline, and events rarely led to treatment discontinuation. The first keratopathy (MEC) event or clinically meaningful BCVA decline recovered in the majority of patients with events. In this ongoing study, patients are being followed for recovery. Based on experience, it is anticipated these events will likely recover over time. Funding: GSK (205678); drug linker technology licensed from Seattle Genetics; mAb produced using POTELLIGENT Technology licensed from BioWa. Disclosures Lonial: Karyopharm: Consultancy; Sanofi: Consultancy; Amgen: Consultancy, Honoraria, Other: Personal fees; Onyx: Honoraria; Takeda: Consultancy, Other: Personal fees, Research Funding; Novartis: Consultancy, Honoraria, Other: Personal fees; Janssen: Consultancy, Honoraria, Other: Personal fees, Research Funding; BMS: Consultancy, Honoraria, Other: Personal fees, Research Funding; GSK: Consultancy, Honoraria, Other: Personal fees; Abbvie: Consultancy; Merck: Consultancy, Honoraria, Other: Personal fees; JUNO Therapeutics: Consultancy; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees; Millennium: Consultancy, Honoraria; Genentech: Consultancy. Nooka:Spectrum Pharmaceuticals: Consultancy; Oncopeptides: Consultancy, Honoraria; Adaptive Technologies: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria, Other: Personal Fees: Travel/accomodations/expenses, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Sanofi: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Karyopharm Therapeutics, Adaptive technologies: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding. Thulasi:Emory University: Current Employment. Badros:University of Maryland: Current Employment; Amgen: Consultancy. Jeng:Kedrion, Merck, GSK: Consultancy; University of Maryland: Current Employment; EyeGate: Current equity holder in publicly-traded company. Callander:University of Wisconsin: Current Employment; Cellectar: Research Funding. Sborov:University of Utah: Current Employment; Celgene, Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Personal fees. Zaugg:University of Utah: Current Employment. Popat:Celgene: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Other: Travel support, Research Funding; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); GSK: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); AbbVie: Consultancy, Honoraria. Degli Esposti:GlaxoSmithKline: Consultancy, Honoraria; Moorfields Eye Hospital: Current Employment. Byrne:Adaptimmune, Novartis: Current equity holder in publicly-traded company; GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Opalinska:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Baron:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Piontek:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Gupta:Novartis: Current equity holder in publicly-traded company; GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Dana:Kala: Consultancy; Alcon: Consultancy; GSK: Consultancy; Aramis Biosciences, Claris Biotherapeutics, GelMEDIX: Current equity holder in private company; Novartis: Consultancy; Dompe: Consultancy; Massachusetts Eye and Ear; Harvard Medical School Department of Ophthalmology: Current Employment; NIH, DOD, Allegan: Current equity holder in publicly-traded company. Farooq:GlaxoSmithKline: Consultancy; University of Chicago: Current Employment. Jakubowiak:Adaptive, Juno: Consultancy, Honoraria; AbbVie, Amgen, BMS/Celgene, GSK, Janssen, Karyopharm: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction: Single-agent belamaf (GSK2857916), a B-cell maturation antigen-targeting antibody-drug conjugate, demonstrated deep and durable responses with a manageable safety profile in patients with heavily pretreated RRMM (median 7 lines of prior therapy) refractory to an immunomodulatory agent (IMiD), a proteasome inhibitor (PI), and refractory and/or intolerant to an anti-CD38 monoclonal antibody in the pivotal Phase II DREAMM-2 study (NCT03525678). At 13-month follow-up, the overall response rate (ORR) was 32% and the median duration of response (DoR) was 11.0 months in the belamaf 2.5 mg/kg arm (Lonial. ASCO 2020 Poster 436). The multimodal mechanism of action, efficacy and safety profile of belamaf, as well as preclinical data suggest possible synergy with standard of care agents and a potential benefit in combination with IMiDs and PIs. DREAMM-6 (NCT03544281) is an ongoing Phase I/II, two-part study of belamaf in combination with lenalidomide/dexamethasone (Arm A) or BorDex (Arm B) in patients with RRMM who had received ≥1 prior therapy (bortezomib-refractory patients were not excluded); preliminary results from Arm B have been reported (Nooka. ASCO 2020 Oral 8502). Methods: Part 1 (dose escalation) and Part 2 (dose expansion) of Arm B in DREAMM-6 evaluated belamaf (2.5 and 3.4 mg/kg intravenously (IV) every 3 weeks [Q3W]) administered as SINGLE (Day 1) or SPLIT dose (divided equally on Days 1 and 8) plus BorDex (Bor 1.3 mg/m2 [subcutaneously] and Dex 20 mg [IV or orally]). Combination treatment continued for up to 8 cycles, with single-agent belamaf maintenance therapy thereafter. Primary objectives were safety, tolerability, and efficacy (ORR [≥ partial response, PR] per investigator-assessed best confirmed response). We report safety and efficacy results from the 2.5 mg/kg SINGLE dose cohort from Arm B. Results: As of March 30, 2020, 18 patients had received belamaf 2.5 mg/kg SINGLE + BorDex in Parts 1 and 2 of Arm B. The median age was 67 years, 61% were male, and 33% had high-risk cytogenetics; patients had received a median of 3 (range, 1-11) prior lines of therapy. All 18 patients had treatment-related adverse events (AEs), of whom 16 (89%) had Grade 3/4 events (see Table). Treatment-related serious AEs occurred in 5 (28%) patients. There were no Grade 5 AEs of interest. Thirteen (72%) patients had dose reductions (8/13 belamaf) and all patients had dose delays (16/18 belamaf) to manage AEs. Five (28%) patients discontinued a study treatment due to AEs: 4 bortezomib, 2 dexamethasone, no patients discontinued belamaf. Of the AEs of interest, thrombocytopenia occurred in 12 patients (67%; maximum Grade 4 in 8 patients and Grade 3 in 3 patients) and led to dose reduction in 6 (33%) patients, dose delay in 7 (39%) patients, and no discontinuations. Three (17%) patients had Grade 2 infusion-related reactions (with no dose modifications or discontinuations). Changes in the corneal epithelium (keratopathy/microcyst-like epithelial changes [MECs], an eye exam finding with or without symptoms), an anticipated AE associated with monomethyl auristatin F, the payload in belamaf, occurred in all 18 patients (maximum Grade 3 in 10 patients, Grade 2 in 7 patients, and Grade 1 in 1 patient), and led to dose reduction in 7 (39%) patients, dose delay in 15 (83%) patients, with no discontinuations. Response was evaluable in all patients; ORR was 78% (95% CI 52.4-93.6), with very good partial response (VGPR) in 9 (50%) and PR in 5 (28%) patients. One (6%) patient had minimal response, and 3 (17%) patients had stable disease. Clinical benefit rate was 83% (95% CI 58.6-96.4). After a median of 18.2 weeks (range 6.0-46.4 weeks) on treatment, median DoR was not reached. Conclusions: The combination of belamaf 2.5 mg/kg Q3W with standard-of care BorDex demonstrated an acceptable safety profile in patients with RRMM who had received a median of 3 prior lines of therapy, with AEs as expected, and no new safety signals to date. Corneal events were common but manageable with belamaf dose modifications. At interim follow-up, best response data indicate a high ORR of 78%, VGPR of 50%, and clinical benefit rate of 83%. Final data for the 2.5 mg/kg SINGLE + BorDex cohort will be reported at the congress. Funding: GSK (Study 207497); drug linker technology licensed from Seattle Genetics; monoclonal antibody produced using POTELLIGENT Technology licensed from BioWa. Disclosures Popat: AbbVie: Consultancy, Honoraria; GSK: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Takeda: Consultancy, Honoraria, Other: Travel support, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria; Celgene: Consultancy, Honoraria. Nooka:Karyopharm Therapeutics, Adaptive technologies: Consultancy, Honoraria, Research Funding; Oncopeptides: Consultancy, Honoraria; Spectrum Pharmaceuticals: Consultancy; Takeda: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Sanofi: Consultancy, Honoraria; Adaptive Technologies: Consultancy, Honoraria; GlaxoSmithKline: Consultancy, Honoraria, Other: Personal Fees: Travel/accomodations/expenses, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding. Stockerl-Goldstein:Celgene: Consultancy; Abbott Laboratories: Current equity holder in publicly-traded company; Abbvie: Current equity holder in publicly-traded company; GSK: Research Funding; Takeda: Research Funding; BiolineRx: Research Funding; Janssen: Research Funding; Cellerant: Other: Other relationship. Abonour:Takeda: Consultancy; Janssen: Honoraria, Research Funding; Celgene: Consultancy; BMS: Consultancy, Research Funding. Khot:Celgene: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Amgen: Other: Speaker fees; Novartis: Other: Travel grant. Lee:Janssen: Consultancy; Amgen: Consultancy; Celgene/BMS: Consultancy. Augustson:Roche: Other: Support of parent study and funding of editorial support. Spencer:AbbVie, Amgen, Celgene, Haemalogix, Janssen, Sanofi, SecuraBio, Specialised Therapeutics Australia, Servier and Takeda: Honoraria; Amgen, Celgene, Haemalogix, Janssen, Servier and Takeda: Research Funding; AbbVie, Celgene, Haemalogix, Janssen, Sanofi, SecuraBio, Specialised Therapeutics Australia, Servier and Takeda: Consultancy; Celgene, Janssen and Takeda: Speakers Bureau. Mateos:Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen-Cilag: Consultancy, Honoraria; PharmaMar-Zeltia: Consultancy; Abbvie/Genentech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Chopra:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Rogers:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Smith:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Davidge:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Montes de Oca:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Ferron-Brady:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Yeakey:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Talekar:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Kremer:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Gupta:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company; Novartis: Current equity holder in publicly-traded company. Quach:Sanofi: Consultancy, Research Funding; Janssen Cilag: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria, Research Funding; Glaxo Kline Smith: Consultancy, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; GlaxoSmithKline: Consultancy, Honoraria, Research Funding.

Introduction: Belamaf (GSK2857916), a B-cell maturation antigen-targeting antibody-drug conjugate (ADC), demonstrated deep and durable responses with a manageable safety profile as a single agent in patients with heavily pretreated RRMM in the pivotal DREAMM-2 study (NCT03525678; Lonial ASCO 2020 Poster 436). Health-related quality of life (HRQoL) was evaluated via the cancer-specific European Organisation for Research and Treatment of Cancer quality of life questionnaire (EORTC-QLQ-C30; Popat EHA 2020 Poster EP1746), a PRO used extensively in oncology/MM studies to evaluate symptoms, functioning, and QoL. The EORTC-QLQ-MY20 module was used to assess MM symptoms. Corneal events are expected during belamaf treatment, as with other monomethyl auristatin F-containing ADCs, so two ophthalmic vision-related PRO questionnaires (National Eye Institute Visual Function Questionnaire-25 item [NEI-VFQ-25] and Ocular Surface Disease Index [OSDI]) were used to characterize the impact of corneal events on patient symptoms and visual function. Meaningful within-patient changes in OSDI and NEI-VFQ-25 scores were estimated to better interpret outcomes in this population (Eliason ISPOR 2020). We report here the results of the PRO analyses in DREAMM-2 according to measures used in the trial. Methods: In DREAMM-2, patients who received single-agent belamaf (2.5 or 3.4 mg/kg, every 3 weeks [Q3W]) completed PRO questionnaires electronically at baseline and Q3W during treatment. Group-level, mean change from baseline over time was evaluated on EORTC domains. We also evaluated the percentage of patients with ≥10-point meaningful change threshold for improvement (Osoba J Clin Oncol 1998) on EORTC domains over time. Meaningful change thresholds in ocular PROs measuring treatment-related corneal events were estimated using recommended anchor and distribution-based methods, with 12.5-16.6 points estimated as meaningful in this population, depending on the domain (Eliason ISPOR EU 2020). We report results of the PRO data analysis for patients in the 2.5-mg/kg group selected for clinical development. Results: At Weeks 7 and 13, 46% (21/46) and 41% (12/29) of patients who completed PROs improved ≥10 points in the EORTC-QLQ-C30 Fatigue domain score, respectively; 30% (14/46) and 31% (9/29) improved their General Pain domain score. For EORTC-QLQ-C30, there were trends toward improvement in Fatigue at some time points on treatment; Global Health Status (GHS)/QoL, Role Functioning, and Physical Functioning domain scores remained relatively stable. The EORTC-QLQ-MY20 Disease Symptoms domain score (representing pain in different locations) showed a general trend toward improvement over time, with improvements of ≥10 points at Weeks 7 and 13 for 38% (17/45) and 29% (8/28) of participants. Ocular PRO data were available for 95% (92/97) of patients. Based on the OSDI vision-related functioning domain, a total of 49.5% of patients experienced a ≥12.5-point worsening from baseline (median time to worsening: 44 days). Meaningful improvement of these changes (based on defined 12.5-point thresholds) from worst severity post baseline was seen in 72% of patients (median time to improvement: 24 days). Importantly, even among patients with meaningful worsening in visual functioning, patient-reported QoL/GHS, Physical Functioning, and Role Functioning domains of the EORTC-QLQ-C30 remained stable while on treatment (Figure). Conclusions: Disease symptoms, functioning, and QoL did not worsen over time in these heavily pretreated patients receiving belamaf in DREAMM-2. Patients showed a general improvement in fatigue, which is often a difficult-to-manage symptom for patients with RRMM. Group-level, meaningful worsening in vision-related PRO domains was observed, which improved in the majority of patients. Despite ocular symptoms, even in patients with meaningful worsening, EORTC-QLQ-C30 data suggest that overall HRQoL and patient functioning remained stable while on treatment. These PRO results demonstrate a balance between overall QoL/functioning and vision-related impacts that, together with its clinical efficacy, supports the use of belamaf in the treatment of patients with RRMM. Funding: GSK (study 205678); drug linker technology licensed from Seattle Genetics; mAb produced using POTELLIGENT Technology licensed from BioWa. Figure 1 Disclosures Popat: GSK: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Celgene: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Other: Travel support, Research Funding; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); AbbVie: Consultancy, Honoraria. Lonial:Novartis: Consultancy, Honoraria, Other: Personal fees; Takeda: Consultancy, Other: Personal fees, Research Funding; Amgen: Consultancy, Honoraria, Other: Personal fees; Sanofi: Consultancy; Karyopharm: Consultancy; GSK: Consultancy, Honoraria, Other: Personal fees; Abbvie: Consultancy; Merck: Consultancy, Honoraria, Other: Personal fees; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees; JUNO Therapeutics: Consultancy; Millennium: Consultancy, Honoraria; Onyx: Honoraria; Genentech: Consultancy; Janssen: Consultancy, Honoraria, Other: Personal fees, Research Funding; BMS: Consultancy, Honoraria, Other: Personal fees, Research Funding. Voorhees:Adaptive Biotechnologies: Other: Personal fees; Levine Cancer Institute, Atrium Health: Current Employment; TeneoBio: Other: Personal fees; Oncopeptides: Other: Personal fees; Novartis: Other: Personal fees; Janssen: Other: Personal fees; Celgene: Other: Personal fees; Bristol-Myers Squibb: Other: Personal fees. Degli Esposti:Moorfields Eye Hospital: Current Employment; GlaxoSmithKline: Consultancy, Honoraria. Gupta:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company; Novartis: Current equity holder in publicly-traded company. Opalinska:GSK: Current Employment, Current equity holder in publicly-traded company. Sapra:GSK: Current Employment, Current equity holder in publicly-traded company. Gorsh:GSK: Current Employment, Current equity holder in publicly-traded company. He:GSK: Current Employment, Current equity holder in publicly-traded company. Kleinman:Triphase Accelerator U.S Corporation: Consultancy; ONL Therapeutics, Inc: Consultancy; Revolution Medicines, Inc: Consultancy; Editas Medicine, Inc: Consultancy; Cleave Therapeutics, Inc: Consultancy; Coherus Biosciences, Inc: Consultancy; Synergy Research Inc: Consultancy; GSK: Consultancy; Eyeon Therapeutics, LLC.: Current equity holder in private company; Zenith Epigenetics Ltd: Consultancy. Schaumberg:Evidera, Inc: Current Employment; GSK: Consultancy; Novaliq: Consultancy; SilkTech: Consultancy; University of Utah School of Medicine: Current Employment. Loubert:Modus Outcomes: Current Employment. Meunier:Modus Outcomes: Current Employment. Regnault:Modus Outcomes: Current Employment. Eliason:GSK: Current Employment, Current equity holder in publicly-traded company.

Introduction: Single-agent belamaf (GSK2857916), a B-cell maturation antigen-targeting antibody-drug conjugate, induced deep and durable responses in patients with RRMM, with a manageable safety profile with 13 months of follow-up (DREAMM-2; NCT03525678; Lonial et al, ASCO 2020, Poster 436). A platform trial design allows efficient evaluation of belamaf in combination with other anti-myeloma agents, such as a humanized wild-type IgG1 anti-OX40 agonist, an IgG4-inducible T-cell co-stimulator (ICOS) agonist, a gamma-secretase inhibitor, and a humanized programmed cell death (PD)-1 antagonist. The unique, multimodal mechanisms of action (MoAs) of belamaf, in combination with MoAs of these agents, has the potential to achieve synergistic effects in RRMM to further enhance anti-myeloma activity without compromising safety. Methods: DREAMM-5 (NCT04126200) is a Phase I/II study that utilizes a master protocol with separate substudies comprised of sequential dose-exploration (DE) and cohort-expansion (CE) phases, to identify promising, effective belamaf combinations when compared with a shared single-agent belamaf control arm (CE phase only). The DE phase consists of multiple dosing cohorts with belamaf combinations in which patients are assigned to treatment slots by a predetermined algorithmic approach (N≤10 per cohort). A recommended Phase II dose (RP2D) for each combination treatment will be identified based on the safety and preliminary efficacy in the DE phase. At the end of the DE phase, an interim analysis of safety, pharmacokinetic, and efficacy data will also be performed for each substudy treatment combination to determine whether the combination should move forward at the RP2D to the CE phase. Patients in the CE phase (N≥35 per cohort) will be randomized to a substudy and within a substudy to either combination treatment or the belamaf monotherapy control arm; patients will also be stratified by number of prior therapies). Eligible patients will have RRMM and will have received ≥3 prior therapy lines, which includes a prior immunomodulatory agent, proteasome inhibitor, and anti-CD38 antibody; all patients will provide informed consent for participation. The primary objectives of the study are to identify the RP2D (DE phase) and the overall response rate (≥partial response, CE phase), along with safety and tolerability, for each combination treatment. Substudies 1 (combination with GSK3174998, OX40 agonist antibody), 2 (combination with GSK3359609, ICOS agonist antibody), and 3 (combination with nirogacestat [PF-03084014; SpringWorks Therapeutics], gamma-secretase inhibitor) are currently open to enrollment. Substudy 4 (combination with dostarlimab; PD-1 antagonist antibody) is under review. Additional substudies will be explored based on scientific rationale and/or preclinical combination study results. Funding: GSK (Study 208887); belamaf drug linker technology licensed from Seattle Genetics; belamaf monoclonal antibody produced using POTELLIGENT Technology licensed from BioWa; nirogacestat gamma-secretase inhibitor produced by and used in collaboration with SpringWorks Therapeutics. Figure: DREAMM-5 study design Figure 1 Disclosures Richardson: Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. Nooka:GlaxoSmithKline: Consultancy, Honoraria, Other: Personal Fees: Travel/accomodations/expenses, Research Funding; Karyopharm Therapeutics, Adaptive technologies: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Spectrum Pharmaceuticals: Consultancy; Adaptive Technologies: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Oncopeptides: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding. Quach:Amgen, sanofi, celgene, Karyopharm, GSK: Research Funding; Amgen, Celgene, karyopharm, GSK, Janssen Cilag, Sanofi.: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline, Karyopharm, Amgen, Celgene, Janssen Cilag: Consultancy; GlaxoSmithKline, Karyopharm, Amgen, Celgene, Janssen Cilag: Honoraria. Trudel:Celgene, Janssen, Takeda, Sanofi, Karyopharm, Amgen Canada: Honoraria; Celgene, Amgen, GSK: Consultancy, Research Funding; GSK, Celgene, Janssen, Amgen, Genentech: Research Funding. Routledge:Celgene, Sandoz: Consultancy; Amgen, BMS, Celgene, Sandoz: Honoraria. Song:Otsuka: Honoraria; Janssen: Honoraria, Research Funding; Amgen, Celgene,Takeda: Consultancy, Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Paul:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Khan:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Brouch:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Ferron-Brady:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Yeakey:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Shelton:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Montes de Oca:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Smith:SpringWorks: Current Employment, Current equity holder in publicly-traded company. Im:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Ahlers:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Paul:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Holkova:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Gupta:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company; Novartis: Current equity holder in publicly-traded company. Kremer:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Rodriguez-Otero:GlaxoSmithKline: Consultancy, Current Employment, Current equity holder in publicly-traded company, Honoraria; Kite: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Oncopeptides: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Medscape: Membership on an entity's Board of Directors or advisory committees; Celgene/Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Sanofi: Consultancy, Honoraria.

Introduction: Belantamab mafodotin (belamaf; GSK2857916) is a B-cell maturation antigen (BCMA)-targeting antibody-drug conjugate. In the pivotal Phase II DREAMM-2 study, single-agent belamaf demonstrated deep and durable responses with a manageable safety profile in heavily pretreated patients with RRMM (Lonial et al. Lancet Oncol 2020). Responses were sustained at 13 months of follow-up; with belamaf (2.5 mg/kg administered intravenously [IV] every 3 weeks [Q3W]), overall response rate (ORR) was 32% and median duration of response (DoR) was 11.0 months (Lonial et al. ASCO 2020 Poster 436). Preclinical data suggest synergistic antimyeloma activity of belamaf in combination with pomalidomide/dexamethasone (Pd). Preliminary data from an ongoing Phase I/II study (NCT03715478) evaluating belamaf in combination with Pd (B-Pd) suggest an acceptable safety profile and early signs of clinical activity in patients with RRMM. The DREAMM-8 study (NCT04484623) will evaluate the efficacy and safety of B-Pd compared with pomalidomide, bortezomib, and dexamethasone (PVd). Methods: This Phase III, two-arm, randomized, open-label, multicenter study will include patients with measurable RRMM who have received ≥1 prior line of therapy (including lenalidomide), with documented disease progression during or after their most recent line of treatment. Patients aged ≥18 years with Eastern Cooperative Oncology Group Performance Status 0-2, adequate organ system function, and who provide informed consent will be eligible. Patients with prior exposure to BCMA-targeted therapies or pomalidomide and those intolerant/refractory to bortezomib will be excluded. Approximately 450 patients will be randomized (1:1) to Arm A (B-Pd) or Arm B (PVd), stratified by number of prior lines of treatment, prior exposure to bortezomib, and International Staging System status. No more than 50% of participants with two or more prior lines of treatment will be enrolled. In Arm A, patients will receive belamaf 2.5 mg/kg (IV) Q4W on Day 1 in Cycle 1 (28-day cycle) followed by belamaf 1.9 mg/kg (IV) Q4W on Day 1 in Cycle 2 onwards (28-day cycles); pomalidomide 4 mg (orally [PO]) will be administered on Days 1-21 and dexamethasone 40 mg (PO) on Days 1, 8, 15, and 22 in all cycles (28-day cycles). In Arm B, pomalidomide 4 mg (PO) will be administered Q3W on Days 1-14 in all cycles (21-day cycles); bortezomib 1.3 mg/m2 will be administered subcutaneously on Days 1, 4, 8, and 11 in Cycles 1-8, and Days 1 and 8 in Cycle 9+ (21-day cycles). Dexamethasone 20 mg (PO) will be administered on the day of and the day after bortezomib. The dose level of dexamethasone in each arm will be reduced by half in patients >75 years of age. Treatment in both arms will continue until progressive disease, unacceptable toxicity, withdrawal of consent, initiation of another anticancer therapy, or end of study or death. The primary endpoint is progression-free survival (PFS; time from randomization to the earliest date of documented disease progression or death [any cause]). Minimal residual disease negativity rate is a key secondary endpoint. Additional secondary endpoints include ORR, time to response, DoR, time to progression, overall survival, PFS2 (PFS after initiation of new anticancer therapy), safety, health-related quality of life, and pharmacokinetic and pharmacodynamic parameters. The study is planned to start in August 2020. Funding: GSK (Study 207499); drug linker technology licensed from Seattle Genetics; mAb produced using POTELLIGENT Technology licensed from BioWa. Disclosures Trudel: GSK, Celgene, Janssen, Amgen, Genentech: Research Funding; Celgene, Janssen, Takeda, Sanofi, Karyopharm, Amgen Canada: Honoraria; Celgene, Amgen, GSK: Consultancy, Research Funding. Davis:GSK: Current Employment, Current equity holder in publicly-traded company. Lewis:GSK: Current Employment, Current equity holder in publicly-traded company. Bakshi:GSK: Current Employment, Current equity holder in publicly-traded company. Chopra:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Montes de Oca:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Ferron-Brady:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Eliason:GSK: Current Employment, Current equity holder in publicly-traded company. Kremer:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company. Gupta:GlaxoSmithKline: Current Employment, Current equity holder in publicly-traded company; Novartis: Current equity holder in publicly-traded company. Wu:GSK: Current Employment, Current equity holder in publicly-traded company.

Multiple myeloma (MM) is a plasma cell malignancy characterized by clonal proliferation of plasma cells within the bone marrow. B cell maturation antigen (BCMA) is a cell-surface receptor required for the survival of plasma cells and is also ubiquitously expressed on MM cells. Belantamab Mafodotin (GSK2857916) is a humanised monoclonal anti-BCMA antibody, which is afucosylated and conjugated to the microtubule-disrupting agent monomethyl auristatin-F (MMAF). Upon binding to BCMA on the cell surface, belatamab mafodotin is rapidly internalised and the cytotoxic moiety (cys-mcMMAF) is released, leading to direct cell death. BCMA is directly shed from the plasma membrane by gamma-secretase, a type-I sheddase. In order to further enhance belantamab mafodotin activity, we sought to increase cell surface levels of BCMA by blocking shedding of BCMA with a gamma-secretase inhibitor (GSI). We then determined the effect on the activity of belantamab mafodotin by combining belantamab mafodotin with PF-03084014, a highly-selective GSI. In order to understand combination effects against immuno-conjugate activity, a 3-day proliferation assay on a panel of multiple myeloma and lymphoma cell lines with varying levels of BCMA expression was conducted. The assay showed a 50 to 3,000-fold EC50 shift in cell lines sensitive to belantamab mafodotin across multiple lymphoma cell types. Antibody-dependent cellular cytotoxicity (ADCC) activity of belantamab mafodotin in combination with PF-03084014 was also examined. In a 24-hour ADCC Jurkat reporter assay, an EC50 shift across multiple BCMA-expressing cell lines was observed. Even cell lines with very low BCMA expression, such as Raji, showed a synergistic increase in ADCC activity in combination with PF-03084014. Cell lines that were non-responsive in the cell proliferation assay, showed activity in the ADCC assay, indicating low-expressing BCMA cell lines remain sensitive to belantamab mafodotin, alone and in combination with PF-03084014. Synergistic effect from this preclinical work provided rationale to support clinical evaluation of belantamab mafodotin in combination with PF-03084014 in a planned clinical trial (DREAMM-5). Disclosures Eastman: GlaxoSmithKline: Employment, Equity Ownership. Shelton:GlaxoSmithKline: Employment, Equity Ownership. Gupta:GlaxoSmithKline: Employment, Equity Ownership. Krueger:GlaxoSmithKline: Employment, Equity Ownership. Blackwell:GlaxoSmithKline: Employment, Equity Ownership. Bojczuk:GlaxoSmithKline: Employment, Equity Ownership.

New treatments are required for rituximab-refractory follicular lymphoma (FL). In the present study, patients with rituximab-refractory FL received 8 weekly infusions of ofatumumab (CD20 mAb; dose 1, 300 mg and doses 2-8, 500 or 1000 mg; N = 116). The median age of these patients was 61 years, 47% had high-risk Follicular Lymphoma International Prognostic Index scores, 65% were chemotherapy-refractory, and the median number of prior therapies was 4. The overall response rate was 13% and 10% for the 500-mg and 1000-mg arms, respectively. Among 27 patients refractory to rituximab monotherapy, the overall response rate was 22%. The median progression-free survival was 5.8 months. Forty-six percent of patients demonstrated tumor reduction 3 months after therapy initiation, and the median progression-free survival for these patients was 9.1 months. The most common adverse events included infections, rash, urticaria, fatigue, and pruritus. Three patients experienced grade 3 infusion-related reactions, none of which were considered serious events. Grade 3-4 neutropenia, leukopenia, anemia, and thrombocytopenia occurred in a subset of patients. Ofatumumab was well tolerated and modestly active in this heavily pretreated, rituximab-refractory population and is therefore now being studied in less refractory FL and in combination with other agents in various B-cell neoplasms. The present study was registered at www.clinicaltrials.gov as NCT00394836.

BACKGROUND: Mutations in isocitrate dehydrogenase (IDH)1 or IDH2 are seen in ~15-20% of patients with acute myeloid leukemia (AML). Mutant IDH (mIDH) reduces α-ketoglutarate to 2-hydroxyglutarate (2-HG), leading to histone hypermethylation and a block in myeloid differentiation, and may also exert leukemogenic effects by inducing dependence on BCL2 and inhibiting homologous recombination. Ivosidenib (AG-120) and enasidenib (AG-221) are oral inhibitors of mIDH1 and mIDH2, respectively, that as monotherapy are associated with robust overall response rates in patients with relapsed/refractory AML. We are assessing the safety and preliminary efficacy of ivosidenib or enasidenib in combination with standard induction chemotherapy. METHODS: In this open-label, multicenter, phase 1 study (NCT02632708), eligible patients with newly diagnosed mIDH1 or mIDH2 AML are treated with standard induction chemotherapy (daunorubicin 60 mg/m2/day or idarubicin 12 mg/m2/day x 3 days with cytarabine 200 mg/m2/day x 7 days) in combination with either ivosidenib 500 mg once daily (for mIDH1) or enasidenib 100 mg once daily (for mIDH2). After induction, patients may receive ≤4 cycles of consolidation chemotherapy while continuing the mIDH inhibitor. Patients who either complete or are ineligible for consolidation may continue on maintenance ivosidenib or enasidenib for ≤2 years from the start of induction. Patients may be removed from the study at any point for an allogeneic hematopoietic stem cell transplant (HSCT); these patients do not receive maintenance therapy post-transplant. RESULTS: As of Apr 18, 2017, 65 patients had been treated: 27 with ivosidenib (median age 60 years, range 24-76) and 38 with enasidenib (median age 63 years, range 32-76, Table 1). Of the 38 patients with mIDH2, 19 (50%) had secondary AML (sAML; arising after myelodysplastic syndrome or another antecedent hematologic disorder, or after exposure to genotoxic injury) compared with 9/27 (33%) with mIDH1. Ivosidenib or enasidenib combined with induction chemotherapy was generally well tolerated. One dose-limiting toxicity was observed (persistent grade 4 thrombocytopenia without leukemia on Day 42 in an enasidenib- and daunorubicin/cytarabine-treated patient). The most frequent grade ≥3 nonhematologic treatment-emergent adverse events during induction therapy, regardless of attribution, in ivosidenib-treated patients were febrile neutropenia (56%), alanine aminotransferase increased (11%), aspartate aminotransferase increased (11%), and colitis (11%); and in enasidenib-treated patients were febrile neutropenia (63%), hypertension (11%), colitis (8%), and maculopapular rash (8%; Table 2). Thirty- and 60-day mortality rates were both 7% in ivosidenib-treated patients, and were 5% and 8%, respectively, in enasidenib-treated patients. Median times for ANC recovery to ≥500/µL were 28 and 34 days for ivosidenib- and enasidenib-treated patients, respectively, and for platelet recovery to >50,000/µL were 28 and 33 days for ivosidenib- and enasidenib-treated patients, respectively. In enasidenib-treated patients with sAML there was an increased time to platelet count recovery (median 50 days). Among 23 efficacy-evaluable ivosidenib-treated patients, a response of CR, CRi, or CRp was achieved in 12/14 (86%) patients with de novo AML and 4/9 (44%) patients with sAML. Among 37 efficacy-evaluable enasidenib-treated patients, a response of CR, CRi, or CRp was achieved in 12/18 (67%) patients with de novo AML and 11/19 (58%) patients with sAML (Table 3). Seven ivosidenib-treated and 14 enasidenib-treated patients received ≥1 cycle of consolidation therapy; 6 ivosidenib-treated and 8 enasidenib-treated patients proceeded to HSCT. CONCLUSION: Ivosidenib or enasidenib in combination with standard AML induction therapy is generally well tolerated. The slower platelet recovery observed in patients with mIDH2 sAML may reflect the reduced normal hematopoietic reserve in sAML patients; nevertheless, alternative dosing schedules for enasidenib with induction chemotherapy are being explored to see if delayed platelet recovery can be mitigated. Response rates thus far are encouraging, especially in patients with sAML, many of whom had received hypomethylating agent therapy. To further understand the quality of responses, analyses of minimal residual disease by mutational clearance are underway. Disclosures Stein: Pfizer: Consultancy, Other: Travel expenses; GSK: Other: Advisory Board, Research Funding; Agios Pharmaceuticals, Inc.: Consultancy, Research Funding; Constellation Pharma: Research Funding; Seattle Genetics: Research Funding; Celgene Corporation: Consultancy, Other: Travel expenses, Research Funding; Novartis: Consultancy, Research Funding. DiNardo: AbbVie: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria, Research Funding; Agios: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Mims: Novartis: Honoraria. Savona: Amgen: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Consultancy, Equity Ownership; Incyte Corporation: Consultancy, Research Funding; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Sunesis: Research Funding; Astex: Membership on an entity's Board of Directors or advisory committees, Research Funding. Stein: Amgen: Consultancy, Speakers Bureau; Stemline: Consultancy. Fathi: Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Medimmune: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Juno: Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria. Stone: Amgen: Consultancy; Abbvie: Consultancy; Novartis: Consultancy; Agios: Consultancy; Ono: Consultancy; Astellas: Consultancy; Arog: Consultancy; Jazz: Consultancy; Celgene: Consultancy; Pfizer: Consultancy; Fuji Film: Consultancy; Sumitomo: Consultancy. Pollyea: Agios, Pfizer: Research Funding; Takeda, Ariad, Alexion, Celgene, Pfizer, Pharmacyclics, Gilead, Jazz, Servier, Curis: Membership on an entity's Board of Directors or advisory committees. Odenike: Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; CTI/Baxalta: Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria; Celgene: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees. Döhner: Agios: Honoraria; Seattle Genetics: Honoraria; Arog Pharmaceuticals: Honoraria, Research Funding; Celator: Honoraria; Amgen: Honoraria; Abbvie: Honoraria; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer Ingelheim: Research Funding; Sunesis: Honoraria; Pfizer: Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Research Funding; Astex Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Schiller: Celator/Jazz: Research Funding. Gupta: Celgene: Employment, Equity Ownership. Nabhan: Agios: Employment, Equity Ownership. Zhang: Agios: Employment, Equity Ownership. Almon: Agios: Employment, Equity Ownership. Cooper: Agios: Employment, Equity Ownership.

Background: Enasidenib (AG-221) is an oral, selective inhibitor of mIDH2 proteins. Results from the AG221-C-001 phase 1/2 dose-escalation and expansion study of enasidenib monotherapy showed an overall response rate (ORR) of 40.3% and median overall survival (OS) of 9.3 months in patients with m IDH2 relapsed or refractory (R/R) AML (Stein, Blood, 2017). Like patients with R/R AML, older patients with untreated AML who are not candidates for standard induction therapy due to advanced age, poor performance status, comorbidities, poor-risk cytogenetics, or other factors, pose a therapeutic challenge. Treatment options for these patients are limited and outcomes are poor. Reported here are clinical outcomes for older patients with previously untreated m IDH 2 AML who received enasidenib monotherapy in the AG221-C-001 study (NCT01915498). Methods: The phase 1 dose-escalation and expansion portions of the study included patients aged ≥ 60 years with previously untreated AML who were not candidates for standard treatment and had ECOG PS scores of 0-2. Patients in the dose-escalation phase received enasidenib doses of 50-650 mg/day, and all patients in the expansion phase received enasidenib 100 mg/day, in continuous 28-day treatment cycles. ORR included complete remission (CR), CR with incomplete count recovery (CRi/CRp), partial remission (PR), and morphologic leukemia-free state (MLFS), per modified IWG 2003 response criteria for AML. OS was defined as the time from first dose to death from any cause. Event-free survival (EFS) was defined as the time from first dose to relapse, progressive disease (PD), or death, whichever came first. Safety was assessed by treatment-emergent adverse event (TEAE) reporting and TEAEs were graded for severity per CTCAE version 4.0. Results: Of 239 patients in the phase 1 dose-escalation and study expansion, 37 patients (15.5%) had previously untreated m IDH2 AML. At data cutoff (14 Oct 2016), 4 patients with previously untreated AML (11%) remained on-study: 3 patients in CR, and 1 patient with stable disease at cycle 13. Median age was 77 years (range 58-87); 62% of patients were aged ≥ 75 years (Table 1). Median number of enasidenib treatment cycles was 6 (range 1-23) and median follow-up was 7.9 months (range 0.5-23.7). Seven patients (19%) attained CR, with a median time to CR of 5.6 months (range 3.4-12.9) (Table 2). ORR was 37.8% (95%CI 22.5, 55.2). The median duration of CR was not reached (NR) (95%CI 3.7, NR) and median duration of any response was 12.2 months (2.9, NR) (Table 2). Three patients proceeded to transplant; at data cutoff, all 3 patients remained in remission. Among all 37 patients, median OS was 10.4 months (95%CI 5.7, 15.1) and median EFS was 11.3 months (3.9, NR). Median OS for responding patients (n=14) was 19.8 months (95%CI 10.4, NR) and for non-responders was 5.4 months (2.8, 12.4). The most frequent TEAEs (any grade or cause) were fatigue (43%), nausea (41%), and decreased appetite (41%). The most frequent treatment-related TEAEs were hyperbilirubinemia (30%) and nausea (22%) (Table 3). The only serious treatment-related TEAEs reported for more than 1 patient were IDH differentiation syndrome (n=3, 8%) and tumor lysis syndrome (n=2, 5%). Treatment-related TEAEs led to dose modification for 3 patients (8%), dose interruption for 7 patients (19%), and treatment discontinuation for 1 patient (3%). Conclusions: Enasidenib induced hematologic responses in these older patients with previously untreated m IDH2 AML who were not candidates for standard treatment. Approximately 1 in 5 of these patients attained CR and 1 in 3 patients had a response with enasidenib monotherapy. Responses were durable: at a median of 7.9 months of follow-up, median CR duration was not reached and median duration of any response was > 1 year. Median OS and EFS were also promising (10.4 months and 11.3 months, respectively). Rates of treatment-related TEAEs were low and only 1 patient discontinued treatment due to a TEAE. These results suggest enasidenib may benefit older adults with m IDH2 AML who are not fit to receive cytotoxic chemotherapy. These encouraging findings have prompted follow-up studies of enasidenib in older patients with previously untreated m IDH2 AML, such as the Beat AML Master Trial (NCT03013998). Disclosures Pollyea: Takeda, Ariad, Alexion, Celgene, Pfizer, Pharmacyclics, Gilead, Jazz, Servier, Curis: Membership on an entity's Board of Directors or advisory committees; Agios, Pfizer: Research Funding. De Botton: Servier: Honoraria; Pfizer: Honoraria; Novartis: Honoraria; Celgene: Honoraria; Agios: Honoraria, Research Funding. DiNardo: Celgene: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Agios: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria, Research Funding. Kantarjian: Bristol-Meyers Squibb: Research Funding; Amgen: Research Funding; Novartis: Research Funding; ARIAD: Research Funding; Pfizer: Research Funding; Delta-Fly Pharma: Research Funding. Collins: BMS: Research Funding; Arog: Research Funding; Agios: Research Funding; Celgene Corporation: Research Funding. Stein: Amgen: Consultancy, Speakers Bureau; Stemline: Consultancy. Xu: Celgene Corporation: Employment, Equity Ownership. Tosolini: Celgene Corporation: Employment, Equity Ownership. Gupta: Celgene Corporation: Employment, Equity Ownership. Agresta: Agios Pharmaceuticals, Inc.: Employment, Equity Ownership. Stein: Seattle Genetics: Research Funding; GSK: Other: Advisory Board, Research Funding; Constellation Pharma: Research Funding; Celgene Corporation: Consultancy, Other: Travel expenses, Research Funding; Agios Pharmaceuticals, Inc.: Consultancy, Research Funding; Pfizer: Consultancy, Other: Travel expenses; Novartis: Consultancy, Research Funding.

Background: Enasidenib (AG-221) and ivosidenib (AG-120) are oral, small-molecule inhibitors of mIDH2 and mIDH1proteins, respectively, both shown preclinically to reduce aberrant 2-HG levels and promote myeloid differentiation. As monotherapies, enasidenib and ivosidenib induce clinical responses in patients (pts) with m IDH relapsed/refractory AML. AZA monotherapy prolonged survival vs conventional care in older pts with newly diagnosed (ND) AML (10.4 vs 6.5 months, respectively; P= 0.101). AZA reduces DNA methylation by inhibiting DNA methyltransferases, and mIDH inhibitors indirectly reduce DNA methylation by suppressing 2-HG and restoring function to α-ketoglutarate-dependent TET family enzymes. In vitro, combinations of mIDH inhibitors + AZA showed synergistic effects on releasing differentiation block in m IDH leukemia models, providing a clinical rationale for combining these agents for treatment (Tx) of AML. Herein we report initial results of the phase 1b portion of an ongoing phase 1b/2 study of mIDH inhibitors + AZA combinations in pts with ND-AML (NCT02677922). Methods: Eligible pts with m IDH ND-AML were aged ≥18 years and ineligible for intensive chemotherapy per investigator assessment. Pts with m IDH2 AML received enasidenib in dose-escalation cohorts of 100 or 200 mg QD and pts with m IDH1 AML received ivosidenib 500 mg QD, each in continuous 28-day cycles. All patients also received SC AZA 75 mg/m2/day x 7 days/cycle. Safety was assessed by Tx-emergent adverse event (TEAE) reporting. Efficacy was assessed per IWG criteria for AML; overall response rate (ORR) included complete remission (CR), CR with incomplete count recovery (CRi/CRp), partial remission (PR), and morphologic leukemia-free state (MLFS). Results: At data cutoff (9 May 2017), 13 pts had received ≥1 dose of enasidenib 100 mg (n=3) or 200 mg (n=3) + AZA, or ivosidenib 500 mg (n=7) + AZA. Ten pts (77%) remained on-study: 2 pts in the enasidenib 100 mg + AZA arm, 2 pts in the enasidenib 200 mg + AZA arm, and 6 pts in the ivosidenib 500 mg + AZA arm. Enasidenib: Median age was 68 years (Table 1). Four pts had de novo AML and 2 pts had secondary AML (sAML). Median number of enasidenib Tx cycles overall was 6.5 (range 1-9). Two pts discontinued Tx due to progressive disease (PD), including 1 pt in the 200 mg arm who later died from a lung infection. The most common (>2 pts) TEAEs were hyperbilirubinemia and nausea (n=3 each). Tx-related TEAEs (any grade) in >1 enasidenib-treated pt were nausea and vomiting (n=2 each).Grade 3-4 TEAEs (any cause) are shown in Table 2. Three serious TEAEs in 1 pt were considered Tx-related: hyperbilirubinemia, febrile neutropenia, and a thromboembolic event in the leg. For enasidenib-treated pts, ORR was 3/6 at data cutoff. In the enasidenib 100 mg + AZA arm, the best responses on-study were 2 CRs; 1 pt had PD. In the enasidenib 200 mg + AZA arm, 1 pt achieved PR and 2 pts maintained stable disease (SD). Ivosidenib: Median age was 81 years (Table 1). Six pts had de novo AML and 1 pt had sAML. Median number of ivosidenib Tx cycles was 4 (range 1-11).TEAEs (any grade) occurring in >2 pts were fatigue (n=6), nausea (5), and constipation (5). Tx-related TEAEs occurring in >1 pt were nausea (n=4) and fatigue (5). The only serious grade 3-4 TEAE occurring in >1 pt was pneumonia (n=2), from which 1 pt died on-study. Neither pneumonia event was considered Tx-related (Table 2). ORR was 3/5; all 3 responders attained CR and 2 pts maintained SD. The remaining 2 pts entered the study in March 2017 and had no response data available at data cutoff. Conclusions: Enasidenib or ivosidenib + AZA combination regimens were generally well tolerated in pts with ND-AML, with 10 of the initial 13 pts remaining on-study at data cutoff, and only 2 discontinuations due to PD. The most common TEAEs with all regimens were grade 1 and 2 GI events and indirect bilirubin increases (likely due to off-target inhibition of UGT1A1 enzyme). Preliminary efficacy results with these combination regimens are encouraging, with 5 CRs and 1 PR on-study. Based on clinical activity and tolerability, the 100 mg enasidenib dose and 500 mg ivosidenib dose will move forward for further study in combination regimens. Evaluation of mIDH inhibitors + AZA continues in 2 currently enrolling randomized studies, including the expansion phase of the current study and the phase 3 AGILE study of ivosidenib + AZA (NCT03173248), to further assess the safety and clinical efficacy of these regimens. Disclosures DiNardo: Novartis: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Agios: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria, Research Funding. Stein: Amgen: Consultancy, Speakers Bureau; Stemline: Consultancy. Fathi: Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Juno: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria; Seattle Genetics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Medimmune: Consultancy, Membership on an entity's Board of Directors or advisory committees. Montesinos: Celgene Corporation: Honoraria, Research Funding. Odenike: Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria; Celgene: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; CTI/Baxalta: Membership on an entity's Board of Directors or advisory committees. Kantarjian: Bristol-Meyers Squibb: Research Funding; ARIAD: Research Funding; Amgen: Research Funding; Delta-Fly Pharma: Research Funding; Novartis: Research Funding; Pfizer: Research Funding. Stone: Fuji Film: Consultancy; Ono: Consultancy; Abbvie: Consultancy; Amgen: Consultancy; Agios: Consultancy; Novartis: Consultancy; Celgene: Consultancy; Pfizer: Consultancy; Astellas: Consultancy; Arog: Consultancy; Jazz: Consultancy; Sumitomo: Consultancy. Koralek: Agios Pharmaceuticals, Inc.: Employment, Equity Ownership. Van Oostendorp: Celgene Corporation: Employment, Equity Ownership. Gong: Celgene Corporation: Employment, Equity Ownership. Gupta: Celgene Corporation: Employment, Equity Ownership. Vyas: Celgene Corporation: Speakers Bureau; Jazz Pharmaceuticals: Speakers Bureau.

Introduction: IDH2 mutations (mIDH2) are recurrent in ~5% of patients (pts) with MDS and ~15% of pts with acute myeloid leukemia (AML). mIDH2 proteins have neomorphic enzymatic activity and are associated with DNA and histone hypermethylation, altered gene expression, and blocked differentiation of hematopoietic progenitor cells. Enasidenib (AG-221/CC-90007) is a small-molecule allosteric inhibitor of mIDH2 protein that induces hematological responses in pts with mIDH2 AML, including relapsed or refractory (R/R) AML (Stein, Clin Cancer Res, 2016). The current analysis is the first to evaluate the safety and clinical efficacy of enasidenib monotherapy in pts with mIDH2-positive MDS. Methods: This analysis includes pts ages ≥18 years with MDS and mIDH2 who participated in a phase 1 study with a dose-finding period followed by an expansion phase in which all pts received daily oral enasidenib 100 mg QD in 28-day cycles. Pts had R/R MDS or were not candidates for standard therapies. Response was measured using peripheral blood (PB) and bone marrow (BM) samples from days 15, 29, 57, and every 56 days thereafter, and by objective investigator report. Overall response rate (ORR) reflects the best response achieved by pts, and includes complete remission (CR), partial remission (PR), marrow CR (mCR), and any hematologic improvement (HI) (IWG 2006 MDS criteria). Evaluable pts required a response assessment at Cycle 2 Day 1 or later, or discontinued before assessment. Overall survival (OS) was estimated using Kaplan-Meier methods. Next-generation sequencing identified pre-existing co-occurring genomic alterations using the FoundationOne® Heme test on purified mononuclear cells from BM or PB, to assess relationships between co-mutational status and clinical response. Results: Of 16 pts with MDS in this study, 12 pts had discontinued and 4 pts continued to receive enasidenib at interim database lock (15 April 2016). Reasons for discontinuation included disease progression (n=1), adverse event (AE; n=1), death (n=4), investigator decision (n=2), and other (n=1); 3 pts proceeded to transplant. Median age was 67 years (range 45-78) (Table 1). R140 mutations were more common than R172 mutations (88% vs 12%). At entry, 3 pts (19%) had relapsed following allogeneic stem cell transplant and 11 (69%) had failed prior treatment (Tx) with a hypomethylating agent (HMA). Six pts (38%) had received ≥2 prior anticancer Tx for MDS. MDS pts in the dose-finding phase received daily enasidenib doses of 60 mg (n=1), 150 mg (1), 200 mg (3), or 300 mg (1); 10 pts received enasidenib 100 mg QD. Median number of Tx cycles was 3 (range 1-25); 5 pts (31%) received ≥6 enasidenib cycles and 4 pts (25%) received ≥12 cycles. Grade 3-4 Tx-emergent AEs (TEAEs) were reported for 13 pts (81%); the most frequent were hyperbilirubinemia (n=5, unconjugated), pneumonia (n=4), thrombocytopenia (n=3) and hypokalemia (n=3). Seven pts (44%) had a grade 3-4 drug-related TEAE. One pt was not evaluable for response. ORR was 53% (8/15), including 1 pt who achieved CR (Figure 1). Of 10 evaluable pts who had received prior HMA Tx, 5 (50%) had a response with enasidenib, including the pt in CR. Of the 4 pts with no prior MDS Tx, 2 responded (1 PR, 1 mCR). Median time to CR, PR, or mCR (sustained ≥4 weeks) was 24 days (range 17-87) from beginning enasidenib Tx, and to HI (sustained ≥8 weeks) was 11 days (11-60). Two pts experienced disease progression. Median OS was not reached after a median follow-up of 4.7 months. FoundationOne® data were available for 12 pts; the most frequently observed known somatic co-occurring mutations were ASXL1 and SRSF2 (Figure 2). Although trends between response and co-occurring ASXL1 and/or SRSF2 mutations were observed, the small number of pts tested prevents definitive conclusions. Discussion: Daily Tx with oral enasidenib monotherapy was well tolerated and induced responses in more than one-half of these MDS pts with mIDH2, 50% of whom had higher-risk disease, and two-thirds of whom had failed prior HMA Tx. Notably, one-half of evaluable MDS pts who had failed prior HMA Tx had a response, including a CR, with enasidenib monotherapy. Only 2 pts experienced disease progression during Tx. Mutational testing is rapidly becoming essential to diagnosis and prognostication in MDS, and assessment of IDH2 mutations can identify MDS pts who may benefit from targeted Tx with enasidenib. Disclosures Stein: Seattle Genetics: Research Funding; Agios Pharmaceuticals: Other: Advisory Board, Research Funding; Celgene: Other: Advisory Board, Research Funding; Novartis: Consultancy. Fathi:Merck: Other: Advisory Board participation; Agios Pharmaceuticals: Other: Advisory Board participation; Seattle Genetics: Consultancy, Other: Advisory Board participation, Research Funding; Celgene: Consultancy, Research Funding; Bexalata: Other: Advisory Board participation. DiNardo:Novartis: Other: advisory board, Research Funding; Agios: Other: advisory board, Research Funding; Celgene: Research Funding; Daiichi Sankyo: Other: advisory board, Research Funding; Abbvie: Research Funding. Pollyea:Celgene: Other: advisory board, Research Funding; Ariad: Other: advisory board; Glycomimetics: Other: DSMB member; Alexion: Other: advisory board; Pfizer: Other: advisory board, Research Funding. Roboz:Celgene: Consultancy; Astex: Consultancy; Agios: Consultancy; Pfizer: Consultancy; Juno: Consultancy; Genoptix: Consultancy; Amgen: Consultancy; MEI Pharma: Consultancy; Janssen: Consultancy; AstraZeneca: Consultancy; Onconova: Consultancy; Sunesis: Consultancy; Novartis: Consultancy; Roche/Genentech: Consultancy; MedImmune: Consultancy; Celator: Consultancy; Amphivena: Consultancy. Sekeres:Amgen Inc.: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Millenium/Takeda: Membership on an entity's Board of Directors or advisory committees. Stone:Pfizer: Consultancy; Sunesis Pharmaceuticals: Consultancy; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy; Amgen: Consultancy; Celator: Consultancy; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Consultancy; Novartis: Consultancy; Jansen: Consultancy; Juno Therapeutics: Consultancy; ONO: Consultancy; Seattle Genetics: Consultancy; Merck: Consultancy; Roche: Consultancy; Xenetic Biosciences: Consultancy. Attar:Agios Pharmaceuticals, Inc.: Employment, Equity Ownership. Tosolini:Celgene: Employment, Equity Ownership. Xu:Celgene: Employment, Equity Ownership. Amatangelo:Celgene: Employment, Equity Ownership. Gupta:Celgene: Employment, Equity Ownership. Knight:Celgene: Employment, Equity Ownership. De Botton:Agios, Celgene, Pfizer, Novartis, Pierre Fabre, Servier: Consultancy, Honoraria, Research Funding. Kantarjian:Amgen: Research Funding; ARIAD: Research Funding; Bristol-Myers Squibb: Research Funding; Pfizer Inc: Research Funding; Delta-Fly Pharma: Research Funding; Novartis: Research Funding.

Background: Despite encouraging progress in treatment results, CLL remains incurable and patients (pts) eventually relapse. Currently, the effects of maintenance therapy are unknown for CLL. OFA, a human anti-CD20 monoclonal antibody, has proven efficacy as a monotherapy in refractory CLL. PROLONG is an open-label, two-arm randomized study of OFA versus observation (obs) for pts in remission after induction treatment for relapsed CLL. Here, we report interim analysis results for the key primary and secondary endpoints of the study. Methods: Pts in CR or PR after 2nd or 3rd line treatment for CLL were randomized 1:1 to receive OFA (300 mg followed 1 week later by 1000 mg every 8 weeks for up to 2 years) or observation. Pts on OFA received premedication with acetaminophen, antihistamine and glucocorticoid. Pts were stratified by number and type of prior therapy, and remission status (CR or PR) after induction treatment. The primary endpoint was progression free survival (PFS) from randomization as assessed by investigator. The predefined interim analysis of efficacy occurred at 2/3 study events (minimum 187), with a p Results: 474 pts were randomized prior to the interim analysis. Baseline characteristics were similar between arms (Table 1). The median duration of OFA treatment was 12.5 months. The median follow-up was 26.1 months for OFA and 24.0 months for obs. The median PFS was 28.6 months for OFA and 15.2 months for obs (HR=0.48; p Adverse events (AEs) during the study occurred in 87% OFA pts vs. 75% obs pts. OFA pts had 25% Grade 3-4 AEs vs. 17% obs pts. Grade3-4 infections were 18% OFA vs. 13% obs. The most common (>5% of all pts) grade 3-4 AEs that occurred were neutropenia (22% OFA vs. 9% obs) and pneumonia (7% OFA vs. 4% obs). Death rate was similar in both arms (14%). AEs that lead to permanent discontinuation of treatment occurred in 8% OFA pts. Conclusions: OFA maintenance provided significant clinical benefit for pts with relapsed CLL. OFA was well-tolerated with no unexpected toxicities. Additional data analyses are ongoing and efficacy outcomes according to patient subgroups will be presented. Acknowledgments: The authors thank the patients for their participation in the study, the other PROLONG investigators, and the HOVON Committee. Figure 1 Figure 1. Figure: Graph of PFS OFA vs. obs Figure:. Graph of PFS OFA vs. obs Disclosures van Oers: Roche: Consultancy. Off Label Use: Ofatumumab is a human anti-CD20 monoclonal antibody that has proven efficacy as monotherapy in refractory CLL. The purpose of its use in this clinical trial is to investigate its use in a maintenance setting for CLL. . Smolej:GlaxoSmithKline: Consultancy, Honoraria, Travel funds Other; Roche: Consultancy, Honoraria, Travel funds, Travel funds Other; Sanofi: Consultancy, Honoraria, Travel funds, Travel funds Other; Janssen: Consultancy, Honoraria, Travel funds, Travel funds Other. Gupta:GlaxoSmithKline: Employment. Phillips:GlaxoSmithKline: Employment. Williams:GlaxoSmithKline: Employment. Lisby:Genmab: Employment. Geisler:Roche: Consultancy; GlaxoSmithKline: Consultancy; Celgene: Consultancy; Janssen: Consultancy.

BACKGROUND: Genomic aberrations and IGHV mutation status are established prognostic factors in CLL. With TP53, NOTCH1, SF3B1, ATM, MYD88, FBXW7, BIRC3 and POT1 recurrently mutated genes were found in CLL and were discussed to associate with disease characteristics and to affect therapy efficacy and outcome. METHODS: We assessed the incidence and impact of gene mutations in the COMPLEMENT1 trial (1st line Chl vs. O-Chl). Pretreatment samples were available from 376 patients (84.1%) and this cohort was representative of the full trial population. Mutations were analyzed by amplicon-based targeted NGS using Illumina Miseq for all coding exons (TP53, ATM, MYD88, FBXW7, BIRC3 and POT1) or hotspot exons (NOTCH1, SF3B1). Additionally, the exact variant frequency was determined. RESULTS: The incidences of gene mutations were: TP53 8.2%, NOTCH1 14.9%, SF3B1 14.1%, ATM 10.9%, MYD88 2.7%, FBXW7 3.5%, POT1 7.7%, and BIRC3 2.7%. Regarding baseline characteristics, we found significant associations: TP53mut with high ß2MG (p=0.01), 17p- (p Regarding response to treatment, TP53mut was significantly associated with reduced ORR rate (p At a median follow-up of 31.7 months, there were 249 (66%) events for PFS and 63 (16.8%) events for OS. O-Chl as compared to Chl resulted in significantly improved PFS (median 22.4 vs. 13.1 months, HR 0.54, p Analyzing both treatment arms separately, TP53mut had an impact on PFS with Chl and O-Chl treatment (HR 1.92, p=0.04 and HR 2.49, p To identify genomic factors of independent prognostic impact, we performed multivariable Cox regression analyses for PFS and OS including treatment arms, 11q-, +12q, 17p-, IGHV and all candidate gene mutations. For PFS, the following independent prognostic factors were identified: O-Chl (HR 0.46, p CONCLUSION: We performed mutational analyses for the 8 most frequent mutated genes in CLL in the COMPLEMENT1 trial evaluating 1st line O-Chl against Chl. An independent prognostic impact was identified for TP53mut, NOTCH1mutand SF3B1mut regarding PFS. Notably, NOTCH1mut affected outcome mainly with O-Chl treatment, whereas ATMmut and BIRC3mut were associated with outcome with Chl monotherapy. In multivariate analysis for OS, none of the gene mutations, but the established parameters IGHV and 17p- had independent prognostic impact. Disclosures Tausch: GlaxoSmithKline: Research Funding, Travel support Other. Hillmen:GSK: Honoraria, Research Funding. Offner:GlaxoSmithKline: Honoraria, Research Funding. Janssens:GSK: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Speakers Bureau; Roche: Speakers Bureau; Mundipharma: Speakers Bureau. Mayer:Glaxo: Research Funding; Roche: Research Funding. Panagiotidis:GlaxoSmithKline: Consultancy, Honoraria. McKeown:GlaxoSmithKline: Employment. Gupta:GlaxoSmithKline: Employment. Stilgenbauer:GlaxoSmithKline: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.

OFA was approved for the treatment of fludarabine and alemtuzumab refractory CLL on the basis of a single-arm study which also included pts with BFR CLL. This open label, randomized, Phase III study of OFA or PC treatment in pts with CLL refractory to fludarabine and with bulky lymphadenopathy (at least one lymph node > 5 cm) was conducted to confirm the results of OFA in BFR pts and also through a 2nd randomization to compare extended OFA (12 months) vs. approved regimen of OFA (6 months). PC was considered an appropriate comparator for these pts given the lack of a consensus around standard of care treatment for this difficult-to-treat population. Pts were randomized 2:1 to receive either the approved regimen of 8 weekly infusions of OFA followed by 4 monthly infusions (Dose 1, 300 mg; Doses 2–12, 2000 mg) or PC of non-OFA containing therapy, including treatments approved for CLL and well established standards of care for up to 6 months. Pts in the OFA arm who had an investigator-assessed CR, PR or SD underwent a 2nd 2:1 randomization to 6 additional OFA infusions 2000 mg every 4 weeks (OFA Ext), or observation (Obs). Pts in the PC arm who developed disease progression during the study could receive OFA salvage therapy for up to 12 months of treatment. Premedication for OFA infusions consisted of glucocorticoid, paracetamol, and antihistamine. The primary objective of this study was to evaluate progression-free survival (PFS) with OFA treatment versus PC as assessed by an Independent Review Committee (IRC). Response assessments were performed using the 2008 Update of the NCI-WG CLL Guidelines [Hallek, 2008]. Secondary endpoints included overall response rate (ORR), time to next therapy (TNT), overall survival (OS), and safety. 122 pts were randomized (79 OFA, 43 PC). Pts completed a median of 12 OFA infusions and 3 months PC therapy. The median PFS (mPFS) as measured by IRC was 5.4 months for OFA and 3.6 months for PC (hazard ratio [HR] 0.79, p=0.27, stratified log rank test; Fig 1). Median PFS as assessed by the investigator (INV) was 7.0 months for OFA and 4.5 months for PC (HR 0.56, p=0.003). The median time to start of next anti-CLL treatment was 11.5 months for OFA and 6.5 months for PC (p=0.0004, stratified log rank test). The ORR (95% CI) by IRC evaluation was 38% (27%, 50%) for OFA and 16% (7%, 31%) for PC (p=0.02). 37 pts underwent a 2nd randomization to either OFA Ext (n=24) or Obs (n=13). From 2nd randomization, mPFS (INV) was 5.6 months for OFA Ext and 3.5 months for Obs (HR: 0.49, p=0.026, stratified log rank test) (Fig 2). Grade ³3 infusion reactions occurred in 5% of pts in the OFA arm with no fatal reactions in either arm. Grade ≥3 cytopenias in the OFA arm included neutropenia (24%, no prolonged neutropenia and 1 patient with late onset neutropenia), thrombocytopenia (8%), anemia (8%). Of the 43 PC pts, 22 received OFA Salvage with an ORR of 50% and mPFS of 5.4 months. Table of Response and Time to event Endpoints OFA (N=79) PC (N=43) Characteristics Median (range) Age, years 61.5 (46 – 82) 63 (40 – 76) No. prior therapies 4 (2 – 16) 3 (2 – 11) No. of infusions 12 (1 – 18) 3 (1 – 6) IRC Investigator Efficacy endpoints OFA PC p-value OFA PC p-value Responders, % 38% 16% 0.019 49% 37% 0.415 mPFS, months 5.36 3.61 0.267 7 4.5 0.003 OFA PC TNT, months 11.5 6.5 p=0.0004 OS, months 19.2 14.5 p=0.13 Figure 1. Kaplan-Meier Estimates of PFS by IRC (OFA vs. PC) Figure 1. Kaplan-Meier Estimates of PFS by IRC (OFA vs. PC) Figure 2. Kaplan-Meier Estimates of PFS by INV (OFA Ext vs. Obs from 2nd randomization) Figure 2. Kaplan-Meier Estimates of PFS by INV (OFA Ext vs. Obs from 2nd randomization) Conclusions: Although the study did not meet its primary endpoint of demonstrating statistically significant superior PFS by IRC, the ORR, PFS by investigator, TNT, and OS favor OFA and were consistent with previously reported results in BFR pts. There was also a longer PFS in pts who underwent the 2nd randomization to receive OFA Ext vs. the approved OFA treatment regimen of 6 months treatment. Disclosures Österborg: GSK: Research Funding. Off Label Use: Discussion of extended ofatumumab dosing (12 months) in addition to the approved 6 month dosing of ofatumumab in refractory CLL. Zaritskey:Novartis: Consultancy, Honoraria. Kaplan:GSK: Honoraria. Steurer:GSK: Consultancy, Honoraria, Research Funding. Schuh:GSK: Honoraria; Roche: Honoraria; Gilead: Honoraria; Celgene: Honoraria; Napp: Honoraria. Montillo:GSK: Honoraria. Kulyaba:GSK: Honoraria. Gorczyca:GSK: Employment. Daly:GSK: Employment. Chai-Ni:GSK: Employment. Lisby:Genmab: Employment. Gupta:GSK: Employment.

Introduction Chemoimmunotherapy with purine analogues and the anti-CD20 antibody rituximab is the standard of care as initial therapy in younger and physically fit patients with chronic lymphocytic leukemia (CLL). However, most CLL patients are elderly and/or have comorbidities, meaning that fludarabine-containing regimens are often inappropriate, carry greater toxicity, and treatment of these patients remains challenging. Most randomized studies in previously untreated CLL have been conducted in younger or fit patients and results cannot necessarily be extrapolated to older, less fit patients. While chlorambucil (CHL) remains a standard of care for this patient population, more effective but tolerable treatment choices are still needed. Ofatumumab (O) demonstrated superior preclinical activity, compared to rituximab, against cells with low CD20 density like CLL and showed clinical activity as monotherapy, with high overall response rates (ORR) in patients with refractory CLL. Therefore, the addition of O to CHL could provide superior clinical outcomes than CHL alone, while being tolerable, for patients who are elderly and/or have comorbidities and currently have limited treatment options. Methods Patients with CLL who required therapy (2008 NCI-WG guidelines) and were considered inappropriate for fludarabine-based therapy due to advanced age and/or co-morbidities were randomized (1:1) to receive either O+CHL or CHL. CHL was given orally (10mg/m2 at days 1-7 of each 28 day cycle) and O was administered as intravenous infusions (Cycle 1: 300mg day 1 and 1000mg day 8, subsequent cycles: 1000mg at day 1). O premedication included acetaminophen, antihistamine and glucocorticoid. Treatment duration was a minimum of 3 cycles, until best response up to a maximum of 12 cycles. The primary endpoint was progression-free survival (PFS) assessed by an Independent Review Committee (IRC) and secondary endpoints included overall response rate (ORR), overall survival (OS) and safety. Patients 447 patients from 16 countries were randomized. Baseline demographics and disease characteristics were well balanced between the 2 arms. Median age was 69 years with 82% ≥65 years and/or having ≥2 comorbidities. All modified Rai stages were represented (Low 8%, intermediate 51%, high 40%). 56% of patients had unmutated IgVH, 6% showed 17p deletions and 75% had β-2-microglobulin levels ≥3500μg/L. Results PFS as assessed by an IRC was significantly prolonged in the O+CHL arm (22.4 months) compared to CHL alone (13.1 months, p Grade ≥3 AEs that occurred from start of treatment until 60 days after the last dose were experienced by 50% of patients receiving O-CHL and 43% of patients on CHL with the most common being neutropenia (O+CHL: 26%, CHL: 14%). Grade ≥3 infusion-related AEs were reported in 10% of patients. No fatal infusion reactions were reported. Grade ≥3 infections were reported in 15% (O+CHL) and 14% (CHL) of patients, with the most common infection being pneumonia (O+CHL: 4%, CHL: 3%). Deaths during treatment occurred in 2% of subjects in both arms. Conclusion Ofatumumab added to chlorambucil (O+CHL) demonstrated clinically important improvements with a manageable side effect profile in patients with CLL who have not received prior therapy and who are considered inappropriate for fludarabine based therapy. Disclosures: Hillmen: Roche Pharmaceuticals: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Pharmacyclics: Research Funding; Celgene: Honoraria; GlaxoSmithKline: Honoraria, Research Funding. Off Label Use: The use of ofatumumab in combination with chlorambucil in previously untreated CLL. The reported trial will support the extension of the ofatumumab licence. Robak:GlaxoSmithKline: Honoraria, Research Funding. Janssens:GlaxoSmithKline: Speakers Bureau; Roche: Speakers Bureau; Mundipharma: Speakers Bureau; Amgen: Speakers Bureau. Mayer:Glaxo: Consultancy, Research Funding; Roche: Consultancy, Research Funding. Panagiotidis:Novartis: Consultancy, Honoraria; Roche: Consultancy, Honoraria; GSK: Consultancy, Honoraria. Kimby:Pharmacyclics: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Teva: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Mundipharma: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Roche: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Emergent: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Schuh:GSK: Honoraria, Research Funding. Montillo:Janssen: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Mundipharma: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; GSK: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Roche: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. McKeown:GSK: Employment. Carey:GlaxoSmithKline: Employment. Gupta:GSK: Employment. Chang:GSK: Employment. Lisby:Genmab: Employment, hold stock options Other. Offner:Lilly: Membership on an entity’s Board of Directors or advisory committees.

Abstract 921 Background: Patients with chronic lymphocytic leukemia (CLL) refractory to fludarabine and alemtuzumab (FA-ref) or refractory to fludarabine with bulky (>5 cm) lymphadenopathy (BF-ref) have poor prognosis with salvage regimens (Tam et al. Leuk Lymphoma 2007). Ofatumumab, a human CD20 monoclonal antibody, was recently approved by the US FDA and EMEA for treatment of CLL refractory to fludarabine and alemtuzumab based on the interim analysis of the pivotal international clinical trial, which included data from 138 patients with FA-ref and BF-ref CLL. At the interim analysis, the overall response rate (ORR; primary endpoint) with single-agent ofatumumab was 58% (99% CI: 40, 74) in the FA-ref group and 47% (99% CI: 32, 62) in the BF-ref group (Wierda et al. J Clin Oncol 2010). Here, we report the final result for the primary endpoint in 206 patients with FA-ref or BF-ref CLL enrolled in this study. Methods: Patients with FA-ref or BF-ref CLL received 8 weekly doses of ofatumumab followed by 4 monthly doses (dose 1, 300 mg; doses 2–12, 2000 mg). Premedication included acetaminophen, antihistamine and glucocorticoid. The primary endpoint (ORR, 1996 NCI-WG criteria) was evaluated over the 24-week treatment period by an Independent Endpoint Review Committee (IRC). Secondary endpoints included duration of response, progression-free survival (PFS), overall survival (OS) and safety. Results: Baseline characteristics are summarized in the Table; 89% and 50% of patients completed 8 and 12 ofatumumab doses, respectively. The ORR (95% CI) by IRC evaluation was 51% (40, 61) for the FA-ref group and 44% (35, 64) for the BF-ref group. Two patients in the BF-ref group achieved complete remission (Table). Results for time-to-event analyses are shown in the Table. Infusion-related AEs occurred in 63% of patients, which primarily occurred during doses 1 and 2, and diminished with subsequent doses. Infusion-related reactions were grade 1–2 events in 95% of patients; no fatal reactions were reported. The most common (≥5% of all patients) grade ≥3 adverse events (AEs) that occurred from start of treatment until 30 days after the last infusion were infections (24%), neutropenia (12%) and anemia (5%). The most common grade ≥3 infection was pneumonia (8% of patients). Fatal infections occurred in 8% of patients (13% in FA-ref; 5% in BF-ref groups). Grade 3–4 thrombocytopenia occurred in 8 patients (4%), febrile neutropenia in 4 patients (2%) and autoimmune hemolytic anemia in 2 patients (1%). Early death (within 8 weeks from start of treatment) occurred in 5 patients (5%) in the FA-ref group (infections, n=5) and 4 patients (4%) in the BF-ref group (infections, n=2; myocardial infarction, n=1; pulmonary edema, n=1). Conclusions: These final results from the pivotal trial clearly demonstrate the efficacy and safety of ofatumumab monotherapy in this heavily pretreated patient population with FA-ref and BF-ref CLL. Additional data analyses are ongoing, and efficacy outcomes for patient subgroups will be presented. Disclosures: Wierda: GlaxoSmithKline: Honoraria, Research Funding. Kipps:GlaxoSmithKline: Research Funding. Mayer:GlaxoSmithKline: Consultancy, Research Funding. Robak:GlaxoSmithKline: Consultancy, Honoraria, Research Funding; Genmab: Consultancy, Research Funding; Roche: Consultancy, Honoraria, Research Funding. Furman:GlaxoSmithKline: Consultancy, Speakers Bureau; Genentech: Consultancy, Speakers Bureau; Cephalon, Inc.: Speakers Bureau; Celegene: Consultancy; Calistoga: Consultancy. Stilgenbauer:Amgen: Research Funding; Bayer: Consultancy, Honoraria, Research Funding; Boehringer-Ingelheim: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Genzyme: Consultancy, Honoraria, Research Funding; GSK: Consultancy, Honoraria, Research Funding; Mundipharma: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding; Sanofi Aventis: Research Funding. Cartron:GlaxoSmithKline: Honoraria; Roche: Honoraria. Padmanabhan:GlaxoSmithKline: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Chan:GlaxoSmithKline: Employment. Gupta:GlaxoSmithKline: Employment. Gorczyca:GlaxoSmithKline: Employment. Davis:GlaxoSmithKline: Employment. Losic:Genmab A/S: Employment, Equity Ownership. Lisby:Genmab A/S: Employment. Österborg:GlaxoSmithKline: Consultancy, Honoraria, Research Funding; Genzyme: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Merck KGaA: Research Funding.