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ZUMA-3 is a phase 1/2 study evaluating KTE-X19, an autologous anti-CD19 chimeric antigen receptor (CAR) T-cell therapy, in adult relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL). We report the phase 1 results. After fludarabine-cyclophosphamide lymphodepletion, patients received a single infusion of KTE-X19 at 2 × 106, 1 × 106, or 0.5 × 106 cells per kg. The rate of dose-limiting toxicities (DLTs) within 28 days after KTE-X19 infusion was the primary end point. KTE-X19 was manufactured for 54 enrolled patients and administered to 45 (median age, 46 years; range, 18-77 years). No DLTs occurred in the DLT-evaluable cohort. Grade ≥3 cytokine release syndrome (CRS) and neurologic events (NEs) occurred in 31% and 38% of patients, respectively. To optimize the risk-benefit ratio, revised adverse event (AE) management for CRS and NEs (earlier steroid use for NEs and tocilizumab only for CRS) was evaluated at 1 × 106 cells per kg KTE-X19. In the 9 patients treated under revised AE management, 33% had grade 3 CRS and 11% had grade 3 NEs, with no grade 4 or 5 NEs. The overall complete remission rate correlated with CAR T-cell expansion and was 83% in patients treated with 1 × 106 cells per kg and 69% in all patients. Minimal residual disease was undetectable in all responding patients. At a median follow-up of 22.1 months (range, 7.1-36.1 months), the median duration of remission was 17.6 months (95% confidence interval [CI], 5.8-17.6 months) in patients treated with 1 × 106 cells per kg and 14.5 months (95% CI, 5.8-18.1 months) in all patients. KTE-X19 treatment provided a high response rate and tolerable safety in adults with R/R B-ALL. Phase 2 is ongoing at 1 × 106 cells per kg with revised AE management. This trial is registered at www.clinicaltrials.gov as #NCT02614066.

Tyrosine kinase inhibitors (TKIs) have improved the outcomes of patients with Philadelphia chromosome positive (Ph+) acute lymphoblastic leukemia (ALL). Many older patients (pts) are not good candidates for intensive chemotherapy and are treated with TKIs plus corticosteroids or low intensity chemotherapy. Although the remission rates with this approach have been high, the median disease-free survival (DFS) has been short. Therefore, novel treatment strategies are needed. This trial evaluated the feasibility of combining the TKI dasatinib with prednisone and blinatumomab in older pts with Ph+ ALL. Methods: This trial was activated through the NCTN in January 2015 and closed to accrual in April 2021. Pt eligibility included: age ≥ 65 years; Ph+ or Ph-like ALL (with dasatinib-sensitive fusions or mutations); newly diagnosed or relapsed/ refractory; no evidence of central nervous system (CNS) disease; and adequate organ function. Treatment: For induction, pts received dasatinib 140 mg/d orally (PO) Days 1-56 along with prednisone 60 mg/m 2/d PO Days 1-24. Pts achieving complete remission (CR) or CR with incomplete count recovery (CRi) (Day 28 or Day 56) continued dasatinib until Day 84 followed by 3 cycles of post-remission therapy (PRT) with blinatumomab/ dasatinib. Pts not achieving CR or CRi by Day 56 received re-induction with blinatumomab. Response was assessed at Day 35 of blinatumomab. Pts not achieving CR/ CRi could receive a second cycle of blinatumomab. This was followed by 3 cycles of PRT with blinatumomab/ dasatinib. Maintenance therapy consisted of prednisone 60 mg/m 2/d x 5 days every 28 days for a total of 18 cycles along with dasatinib 140 mg po qd indefinitely. CNS prophylaxis included intrathecal (IT) methotrexate every 4-6 weeks x 8 doses. IT methotrexate was given at least 2 days apart from blinatumomab. Response was assessed at Days 28, 56, 84 and additional time points were dependent on response. Minimal residual disease (MRD) was assessed centrally by multi-color flow cytometry at Day 28. Statistics: 9 eligible/ evaluable pts receiving PRT were to be evaluated before enrolling additional pts. Dose-limiting toxicities (DLTs) were defined as: > Grade 3 non-hematologic toxicities with the exception of nausea, vomiting, or diarrhea (if manageable with supportive care measures) or Grade 4 neutropenia lasting > 42 days with possible relationship to dasatinib or blinatumomab. If due to unexpected accrual, 12 pts were evaluable for DLT, the following rules would apply. If > 4 of the 12 pts experienced a DLT, the study would be temporarily closed pending review. Upon re-opening, 8 additional eligible and evaluable pts would be enrolled for a total of 20 pts receiving blinatumomab. Results: Due to rapid accrual, 16 pts enrolled before accrual was paused to assess feasibility and safety. Twelve pts were evaluable for DLT and 4 experienced a DLT: Grade 3 dyspnea and gastrointestinal pain (n=1), Grade 3 hypertension (n=1), Grade 3 dyspnea (n=1), Grade 3 hyperglycemia (n=1). These adverse events were deemed acceptable by the NCI and FDA and the study re-opened. A total of 25 eligible pts were accrued. The median age was 73 years (range 62-87). All pts were newly diagnosed. One pt was Ph-like, with the remainder being Ph+; 89% of Ph+ pts had additional cytogenetic abnormalities. During induction, 2 pts experienced treatment-related non-hematologic Grade 4 toxicities. No Grade 4 or higher treatment-related non-hematologic toxicities occurred during post-remission therapy or maintenance. Twenty-three out of 25 pts (92%) achieved a CR during dasatinib-based and prednisone induction therapy. Four did not receive PRT (2 due to adverse events, 1 to receive transplant, 1 because of insurance issues). Sixteen pts who achieved CR had MRD data. Five out of 16 pts (31%) were MRD negative at Day 28. One pt remains on PRT and 10 are on maintenance. The median follow up for pts who are alive is 1.7 years. The median overall survival (OS) and DFS have not been reached as of July 8, 2021. Kaplan-Meier 3-year estimates of OS and DFS are 85% (95% CI 58%-95%) and 80% (95% CI 55%-92%), respectively (Figure). Conclusions: This trial demonstrates the feasibility of combining dasatinib and blinatumomab in Ph+ ALL. In addition, with 1.7 years of follow up, outcomes are encouraging with high estimated 3-year DFS and OS. Longer follow up will be needed to determine the durability of these results. Figure 1 Figure 1. Disclosures Advani: Kite Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Research Funding; Glycomimetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Immunogen: Research Funding; OBI: Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Research Funding; Macrogenics: Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Moseley: BioSight Ltd: Consultancy. Wood: Pfizer, Amgen, Seattle Genetics: Honoraria; Juno, Pfizer, Amgen, Seattle Genetics: Other: Laboratory Services Agreement. Park: Intellia: Consultancy; Kura Oncology: Consultancy; BMS: Consultancy; Affyimmune: Consultancy; Curocel: Consultancy; Novartis: Consultancy; Artiva: Consultancy; PrecisionBio: Consultancy; Servier: Consultancy; Kite Pharma: Consultancy; Innate Pharma: Consultancy; Minerva: Consultancy; Autolus: Consultancy; Amgen: Consultancy. Wieduwilt: Gilead: Membership on an entity's Board of Directors or advisory committees; Reata: Current holder of stock options in a privately-held company. Jeyakumar: Jazz: Research Funding; Pfizer: Research Funding. Atallah: Abbvie: Consultancy, Speakers Bureau; BMS: Honoraria, Speakers Bureau; Takeda: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Amgen: Consultancy. Gerds: PharmaEssentia Corporation: Consultancy; CTI BioPharma: Research Funding; Sierra Oncology: Consultancy; AbbVie: Consultancy; Celgene/Bristol Myers Squibb: Consultancy; Constellation: Consultancy; Novartis: Consultancy. O'Brien: Amgen, Astellas, Celgene, GlaxoSmithKline, Janssen Oncology, Aptose Biosciences Inc., Vaniam Group LLC, AbbVie, Alexion, Verastem, Juno Therapeutics, Vida Ventures, Autolus, Johnson and Johnson, Merck, Bristol Myers Squibb, NOVA Research Company, Eli Lill: Consultancy; Kite, Regeneron, Acerta, Caribou, Gilead, Pharmacyclics, TG Therapeutics, Pfizer, Sunesis: Research Funding. Othus: Celgene: Other: Data safety monitoring board; Merck: Consultancy; Biosight: Consultancy; Glycomimetics: Other: Data safety monitoring board; Daiichi Sankyo: Consultancy. Litzow: Jazz: Other: Advisory Board; Pluristem: Research Funding; Amgen: Research Funding; Actinium: Research Funding; Omeros: Other: Advisory Board; Astellas: Research Funding; AbbVie: Research Funding; Biosight: Other: Data monitoring committee. Stone: Actinium: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; Arog: Consultancy, Research Funding; Astellas: Membership on an entity's Board of Directors or advisory committees; BerGen Bio: Membership on an entity's Board of Directors or advisory committees; Boston Pharmaceuticals: Consultancy; Bristol Myers Squibb: Consultancy; Elevate Bio: Membership on an entity's Board of Directors or advisory committees; Foghorn Therapeutics: Consultancy; Gemoab: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Consultancy; Innate: Consultancy; Janssen: Consultancy; Jazz: Consultancy; Novartis: Consultancy, Research Funding; Onconova: Consultancy; Syndax: Membership on an entity's Board of Directors or advisory committees; Syntrix/ACI: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees; Aprea: Consultancy; Amgen: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy; Agios: Consultancy, Research Funding; Celgene: Consultancy; Macrogenics: Consultancy. Erba: AbbVie Inc; Agios Pharmaceuticals Inc; ALX Oncology; Amgen Inc; Daiichi Sankyo Inc; FORMA Therapeutics; Forty Seven Inc; Gilead Sciences Inc; GlycoMimetics Inc; ImmunoGen Inc; Jazz Pharmaceuticals Inc; MacroGenics Inc; Novartis; PTC Therapeutics: Research Funding; AbbVie Inc; Agios Pharmaceuticals Inc; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Incyte Corporation; Jazz Pharmaceuticals Inc; Novartis: Speakers Bureau; AbbVie Inc: Other: Independent review committee; AbbVie Inc; Agios Pharmaceuticals Inc; Astellas; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Daiichi Sankyo Inc; Genentech, a member of the Roche Group; GlycoMimetics Inc; Incyte Corporation; Jazz Pharmaceuticals Inc; Kura Oncology; Nov: Other: Advisory Committee.

Background: Somatic mutations in the IDH genes are common in acute myeloid leukemia (AML). Mutations occur at active site arginine residues in IDH1 (R132) and IDH2 (R140, R172). IDH inhibitors, ivosidenib (IDH1) and enasidenib (IDH2), have shown improved clinical outcomes in patients with relapsed/refractory IDH-mutant AML and are approved for use in this setting, while investigations in combination with chemotherapy are underway in de novo AML. The prognostic significance of IDH mutations remains controversial. We hypothesize that refining our understanding of IDH-mutated AML will contribute to risk-adapted treatment strategies, including optimal use of IDH-targeted agents. The objective of our study was to identify characteristics that affect outcome in de novo IDH-mutated AML across the age spectrum utilizing a large cohort of patients enrolled on several pediatric and adult trials. Methods: The total cohort (N=3588) included patients age Results: The prevalence of IDH mutations among the entire cohort was 8.6% (N=276). Analysis according to mutation type demonstrated that IDH2 mutations comprised 57% (N=158) and IDH1 mutations 43% (N=118). The prevalence of IDH mutations was strongly correlated with increased age (Fig 1A); according to the age-defined cohorts was 4.0% (N=82) in younger, 15.2% (N=126) in intermediate, and 20.3% (N=65) in older patients (p Conclusion: Analysis of this large patient cohort provides the most comprehensive description of IDH mutations in AML across the age spectrum. We confirm age-associated prevalence of IDH mutations and frequent co-occurrence with NPM1 mutation in all ages and in further combination with DNMT3A mutation in intermediate-aged adults. We definitively demonstrate that IDH mutation status is not an independent prognostic determinant of outcome in any age group. Co-occurrence of NPM1 and IDH mutations favorably impacts outcome in patients < 60 years of age with AML, particularly in the absence of DNMT3A mutation. Our data support that IDH inhibitors may be of particular interest in older adults and in patients Disclosures Othus: Marck: Consultancy; Daiichi Sankyo: Consultancy; Celgene: Membership on an entity's Board of Directors or advisory committees; Glycomimetics: Membership on an entity's Board of Directors or advisory committees. Radich:Jazz: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding; Amgen: Consultancy; Bristol-Myers Squibb: Consultancy. Abdel-Wahab:Merck: Consultancy; Janssen: Consultancy; Envisagenics Inc.: Current equity holder in private company; H3 Biomedicine Inc.: Consultancy, Research Funding. Tallman:UpToDate: Patents & Royalties; ADC Therapeutics: Research Funding; BioSight: Membership on an entity's Board of Directors or advisory committees, Research Funding; Glycomimetics: Research Funding; Rafael: Research Funding; Amgen: Research Funding; Bioline rx: Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Membership on an entity's Board of Directors or advisory committees; KAHR: Membership on an entity's Board of Directors or advisory committees; Rigel: Membership on an entity's Board of Directors or advisory committees; Delta Fly Pharma: Membership on an entity's Board of Directors or advisory committees; Oncolyze: Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Abbvie: Research Funding; Cellerant: Research Funding; Orsenix: Research Funding. Atallah:Jazz: Consultancy; Genentech: Consultancy; Abbvie: Consultancy; Takeda: Consultancy, Research Funding; Pfizer: Consultancy; Novartis Pharmaceutical Corporation: Consultancy. Luger:Daiichi-Sankyo: Honoraria; Pfizer: Honoraria; Bristol-Myers Squibb: Honoraria; Acceleron: Honoraria; Agios: Honoraria; Loxo Oncology: Honoraria; Onconova: Research Funding; Kura: Research Funding; Biosight: Research Funding; Ariad: Research Funding; Hoffman La Roche: Research Funding. Levine:Novartis: Consultancy; Loxo: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Morphosys: Consultancy; Astellas: Consultancy; Janssen: Consultancy; Prelude Therapeutics: Research Funding; Amgen: Honoraria; Gilead: Honoraria; Lilly: Consultancy, Honoraria; Qiagen: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Imago: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; C4 Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Isoplexis: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding. Cooper:Celgene: Other: Spouse was an employee of Celgene (through August 2019).

Introduction AML primarily affects older adults and long-term survival in this group is poor. Despite data showing improvement in outcomes of adults aged Methods We performed a retrospective analysis of consecutive patients aged ≥60 evaluated at an academic cancer center between Jan 2014 and Dec 2017. We included patients who were diagnosed and received all treatment at our center (N=101), as well as patients referred from outside institutions for HSCT who did not receive initial treatment at our center (N=12). We collected demographics, disease and treatment characteristics, responses, and outcomes. For patients diagnosed and treated at our center, we determined whether discussion about HSCT was documented, rates of HSCT referral and utilization, and time from diagnosis to HSCT referral and utilization. For patients who were referred for HSCT only, we determined HSCT rates and time from diagnosis to HSCT. Fisher's exact test was used to assess the association of patient factors with HSCT referral and utilization. A Cox model was used to assess the association of HSCT (via a time-dependent covariate) with relapse-free survival (RFS) and overall survival (OS). Results Median age was 70 years (IQR 10), 53% were male, and 91% were white. Among patients who were diagnosed and received all treatment at our center, 30% (N=30/101) were referred for HSCT, and 20% (20/101) received HSCT. Among patients who were referred from outside institutions, 42% (N=5/12) received HSCT. Thirty-seven percent (N=37/101) had a documented discussion regarding HSCT and referral was made for 81% (N=30/37). Common documented reasons (can be multiple) for not referring a patient were: performance status (N=20), advanced age (N=15), patient refusal (N=13), refractory disease (N=11), and prohibitive comorbidity (N=6). Reasons were not documented in 22 patients. Among the patients who were referred but did not receive HSCT (N=10/30), common documented reasons for not proceeding with HSCT were: refractory disease (N=5), advanced age (N=2), and prohibitive comorbidity (N=1). HSCT referral and utilization rates decreased with increasing age (Figure 1a) and were similar from 2014-2017 (Figure 1b). Patients referred for HSCT were more likely to be younger (median 66.0 vs 73.0 years, p Conclusions Our study highlights that HSCT referral and utilization rates for older adults with AML are low and have not increased over time, despite improvement in supportive care, reduced intensity conditioning regimens, and alternate donor sources. Less than half of older patients who received intensive induction therapy were referred for HSCT. We suspect that the increasing use of effective lower intensity therapies will affect these rates as more patients achieve remission without intensive induction. Strategies are needed to improve referral and HSCT rates for older adults, such as formalized fitness assessments, interventions to improve performance status, and more effective therapies to reduce relapse rates. In addition, larger prospective studies are needed to evaluate the utility of HSCT in older adults with AML. Disclosures Mendler: Jazz Pharmaceuticals: Speakers Bureau; GLG: Consultancy. Aljitawi:Sanatela Medical: Patents & Royalties: Patent pending. Liesveld:Abbvie: Honoraria; Onconova: Other: data safety monitoring board. Loh:Seattle Genetics: Consultancy; Pfizer: Consultancy.

Introduction: EOL care in patients (pts) with hematologic malignancies (HM) has been inadequately studied. Available data suggest that pts with HM are more likely to be hospitalized and receive chemotherapy at EOL, and less likely to be enrolled in hospice relative to pts with solid tumors. Better understanding of the barriers to high-quality EOL care is needed for HM pts. The aim of this study was to identify potential barriers to high-quality EOL care for pts with AML and MDS. Methods: We conducted a retrospective study of pts aged ≥18 years with AML or MDS who were evaluated at Wilmot Cancer Institute and its affiliates, and died between Jan 1, 2014 and Dec 31, 2019. We collected the following EOL metrics: 1) Hospice enrollment; 2) Palliative care (PC) referral; 3) MOLST form completion and do-not-resuscitate orders; 4) Chemotherapy administration within the last 14 days of life; 5) Utilization of the emergency department (ED), hospital, intensive care unit (ICU), and life-sustaining treatments (LSTs) within the last 30 days of life; 6) Transfusion within the last 7 days of life; 7) Place of death; and 8) Time from MOLST form completion, PC referral, and hospice enrollment to date of death. Fisher's exact tests were used to compare EOL metrics between pts with MDS and AML. We used cumulative incidence functions to estimate the probability of PC referral and MOLST form completion within 12 weeks of the first hematology visit, accounting for the competing risk of death. We analyzed the univariate and multivariate associations of timing (>30 days vs never/30 days prior to death) of MOLST form completion, PC referral, and hospice enrollment with utilization of the ED, hospital, ICU, and LSTs at EOL. We evaluated the associations of MOLST form completion, PC referral, and hospice enrollment with hospital death. Results: We included 120 pts with MDS (mean age 73.6; range 25-93) and 238 pts with AML (mean age 65.7; range 20-95). EOL metrics by diagnosis are shown in Table 1. The probability of PC referral within 12 weeks of the first hematology visit was 16.7% [95% Confidence Interval (CI) 12.2-21.9%] and 7.1% (95% CI 3.3-12.9%) for AML and MDS, respectively. The probability of MOLST form completion within 12 weeks of the first hematology visit was 23.7% (95% CI 18.3-29.4%) and 11.9% (95% CI 6.7-18.8%) for AML and MDS, respectively. A MOLST form was completed early (>30 days before death) in 33.3% (N=115/345) of pts. In univariate analysis, these pts were less likely to be hospitalized (78.1 vs 89.3%, p30 days before death) occurred in 3.8% (N=13/340) of pts. In univariate analysis, these pts were less likely to visit the ED (0 vs 46.6%, p30 days before death) occurred in 21.4% (N=73/341) of pts and was not associated with EOL metrics in univariate analysis. In multivariate analysis, after adjusting for age and diagnosis, early MOLST form completion was associated with a lower risk of ICU admission [Odds Ratio (OR) 0.23, p Conclusion: We found a high rate of ED visits, hospitalizations, ICU admissions, and use of LSTs at EOL in pts with MDS and AML. The majority of these pts died in the hospital. While most patients completed MOLST forms and had palliative care referrals, these events generally occurred very late in the disease course, often close to EOL. Early MOLST form completion and early hospice enrollment were associated with better EOL quality metrics. Interventions to promote timely completion of orders for life-sustaining treatment, PC referrals, and hospice enrollments may improve EOL care among pts with AML and MDS. Table Disclosures Loh: Pfizer: Consultancy; Seattle Genetics: Consultancy. Liesveld:Abbvie: Honoraria; Onconova: Other: data safety monitoring board. Aljitawi:Sanatela Medical: Patents & Royalties: Patent pending. Mendler:Jazz Pharmaceuticals: Speakers Bureau; GLG: Consultancy.

Most cancers evolve over time as patients initially responsive to therapy acquire resistance to the same drugs at relapse. Cancer stem cells have been postulated to represent a therapy-refractory reservoir for relapse, but formal proof of this model is lacking. We prospectively characterized leukemia stem cell populations (LSCs) from a well-defined cohort of patients with acute myelogenous leukemia (AML) at diagnosis and relapse to assess the effect of the disease course on these critical populations. Leukemic samples were collected from patients with newly diagnosed AML before therapy and after relapse, and LSC frequency was assessed by limiting dilution analyses. LSC populations were identified using fluorescent-labeled cell sorting and transplantation into immunodeficient NOD/SCID/interleukin 2 receptor γ chain null mice. The surface antigen expression profiles of pretherapy and postrelapse LSCs were determined for published LSC markers. We demonstrate a 9- to 90-fold increase in LSC frequency between diagnosis and relapse. LSC activity at relapse was identified in populations of leukemic blasts that did not demonstrate this activity before treatment and relapse. In addition, we describe genetic instability and exceptional phenotypic changes that accompany the evolution of these new LSC populations. This study is the first to characterize the evolution of LSCs in vivo after chemotherapy, identifying a dramatic change in the physiology of primitive AML cells when the disease progresses. Taken together, these findings provide a new frame of reference by which to evaluate candidate AML therapies in which both disease control and the induction of more advanced forms of disease should be considered.

Adolescents and young adults (AYAs) form a unique group of patients with newly diagnosed acute myeloid leukemia (AML). They differ in terms of disease biology, psychosocial challenges, survival, and in other important respects from children as well as from middle-aged and older adults. AYAs may be treated using pediatric protocols developed in trials composed primarily of younger patients, or using adult protocols developed in trials composed primarily of older patients. After reviewing the distinguishing characteristics of AYAs with AML, we compare and contrast the chemotherapy approaches and argue that neither the pediatric nor adult approaches may be ideally suited for AYAs and the development of AYA-specific approaches merits further consideration. We finish by putting forth ideas for future research to optimize chemotherapy treatment of AYAs with AML.

The prognosis of patients (pts) with relapsed/ refractory acute lymphoblastic leukemia (ALL) remains poor and novel therapies are needed. The anti-CD22 immunoconjugate inotuzumab ozogamicin (IO) has demonstrated promising results in phase 2 and 3 trials. Pre-clinical studies have demonstrated superior anti-tumor activity when IO is co-administered with cyclophosphamide (C), vincristine (V), and prednisone (P). We assessed the safety of IO in combination with CVP and determined the maximum tolerated dose (MTD) of IO in this regimen for pts with relapsed or refractory (R/R) CD22+ acute leukemia. An expansion cohort was treated at the MTD and efficacy results are presented. Methods: Pts were treated at SWOG institutions from 2014-19. IO was supplied by Pfizer. Eligibility: age > 18 yrs, > 20% blasts expressing CD22, R/R CD22+ acute leukemia (B-ALL, mixed phenotype, or Burkitts), and adequate organ function. All pts received C (750 mg/m2) intravenous (IV) Day (D) 1, V (1.4 mg/m2) (max 2 mg) IV D1, P (100 mg) orally D 1-5 and IO (dose escalated as in Table 1) up to a maximum of 6 cycles. Each cycle was 28 d. Dose escalation utilized a standard 3+3 design with the plan to treat 12 additional pts at the MTD. Dose limiting toxicities (DLTs) were considered: (1) > Grade (Gr) 4 non-hematologic toxicities (NHTs) with the exception of nausea, vomiting and toxicities secondary to neutropenia and sepsis; (2) prolonged myelosuppression [absolute neutrophil count < 500/ uL or platelet count < 25,000/uL] in a bone marrow with < 5% blasts and no evidence of leukemia that lasts > 35 d beyond the last dose of IO; (3) any Gr 3 NHT (excluding peripheral neuropathy, hyperglycemia, and toxicities secondary to neutropenia, thrombocytopenia, and sepsis) that does not resolve to < Gr 2 by 7 d beyond the last dose of IO; (4) any > Gr 3 elevation in SGOT/ SGPT or bilirubin lasting > 7 d; (5) any IO-related toxicity resulting in permanent discontinuation of IO. Results: 50 pts were enrolled; 2 were ineligible. The median age was 43 yrs (range 20-79), 56% were male, and the median WBC at registration was 2.7 K/uL (range 0.3-59.6). All pts had B-ALL. The median time from initial diagnosis to registration was 515 d. Twenty-one pts were in 1st relapse, 12 in 2nd relapse, 4 in 3rd relapse, 1 in 4th relapse, and 10 pts were refractory to their last treatment. Eighteen pts (38%) had received prior blinatumomab; 9 had prior allogeneic hematopoietic stem cell transplant (AHSCT); 30% had poor risk cytogenetics (Ph+, -7, +8, complex, MLL abnormalities, or hypodiploid); 13 pts were tested for the Ph-like signature with 5 pts identified as Ph-like. One death occurred during treatment and was attributed to pneumonia in the setting of active ALL. Gr 3-4 hematologic toxicity related to treatment was common: neutropenia (73%), thrombocytopenia (63%), and anemia (50%). Gr 3-4 NHTs were mainly febrile neutropenia. One DLT occurred at DL 3: prolonged myelosuppression and 1 DLT at DL 5: Gr 3 ascites. Gr 3-4 transaminases or bilirubin occurred in 1 pt (2%) during treatment and in 10 pts (23%) during follow-up. No cases of hepatic veno-occlusive disease (VOD) occurred during treatment but 3 (7%) occurred during follow up (post-transplant). The MTD was DL 5. Thirteen pts (30%) proceeded to AHSCT after study treatment. The complete remission (CR)/ CR with incomplete count recovery rate was 61% (95% CI 39%-80%) in the 23 evaluable pts treated at the MTD, and 60% (3/ 5) in pts with the Ph-like signature. There was no statistically significant difference in response rates or hepatic toxicities between the various DLs. However, all 3 VOD cases occurred either after 2nd transplant (n=2) and/ or at DL 5 (n=2). The rates of CR/CRi were 60% and 50% respectively in DLs 1 and 2. The median overall survival was 7.7 months for all pts, and 10.9 months for pts treated at the MTD. Notably, 1 pt remains in a remission 3.5 yrs out from registration without having a transplant. Conclusion: CVP/IO is relatively well tolerated with high response rates and low toxicity despite a heavily pre-treated group of pts. Minimal residual disease data and additional Ph-like signature data are being compiled. Randomized studies will be needed to determine differences in toxicities and response rates with the various doses. However, there is a suggestion that VOD may increase with higher doses of IO and in the setting of 2 transplants. This regimen may represent a promising strategy in the treatment of elderly pts in the newly diagnosed setting. Disclosures Advani: Abbvie: Research Funding; Macrogenics: Research Funding; Glycomimetics: Consultancy, Research Funding; Kite Pharmaceuticals: Consultancy; Amgen: Research Funding; Pfizer: Honoraria, Research Funding. Liedtke:Prothena: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; IQVIA/Jazz: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech/Roche: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celator: Research Funding; Caelum: Membership on an entity's Board of Directors or advisory committees; BlueBirdBio: Research Funding; Amgen/Onyx: Consultancy, Honoraria, Research Funding; Adaptive: Membership on an entity's Board of Directors or advisory committees; Agios: Research Funding. Aldoss:Jazz Pharmaceuticals: Honoraria, Other: travel/accommodation/expenses, Speakers Bureau; Agios: Consultancy, Honoraria; AUTO1: Consultancy; Helocyte: Consultancy, Honoraria, Other: travel/accommodation/expenses. Othus:Celgene: Other: Data Safety and Monitoring Committee; Glycomimetics: Other: Data Safety and Monitoring Committee. Erba:Amgen, Celgene, Daiichi Sankyo, ImmunoGen, Incyte, Jazz Pharmaceuticals, Millennium, Novartis, Ono, Pfizer, Seattle Genetics, Sunesis: Consultancy; Celgene, Incyte, Novartis: Speakers Bureau; Agios, Amgen, Astellas Pharma, Daiichi Sankyo, ImmunoGen, Janssen, Jazz Pharmaceuticals, Juno, Millennium, Seattle Genetics: Research Funding.

Background: Relapse remains the most common cause of treatment failure after intensive induction and consolidation (CONS) therapy in older adults with AML. We therefore performed a prospective randomized phase II study to determine the safety and impact on DFS (relapse or death) and OS of DAC maintenance using an abbreviated 3-day schedule administered every 4 weeks for 1 year (per Lubbert et al, Haematologica 97:393, 2012) vs. Observation (OBS) after intensive AML therapy, conducted in the large multi-center E-A E2906 Phase III trial in patients (pts) age ≥60 yrs. Methods: The design and primary clinical results for E2906 (n=727) have been reported previously (Foran et al, ASH #217a, 2015), demonstrating superior OS following 'Standard' 7&3 (Daunorubicin 60mg/m2) induction and intermediate dose Ara-C consolidation (CONS) vs. single agent Clofarabine (CLO, provided by SANOFI), despite similar CR/CRi (CR with incomplete CBC recovery) and induction mortality rates. All CR/CRi pts after induction (n=311) were assigned to 2 cycles CONS with either Ara-C (1.5g/m2 x 12 doses; 6 doses if age >/=70 yrs), or single agent CLO, based on induction randomization. Ongoing CR/CRi after recovery from CONS was confirmed with restaging BM biopsy, and eligible pts offered participation in the 'Step 3' maintenance study, a 1:1 randomization (stratified by induction therapy, cytogenetic risk group, age 'Step 3' was designed as a phase II pilot randomized study, with target accrual n=172, allowing 90% power to detect 36% reduction in DFS Hazard Ratio (HR) with DAC maintenance for 1 year (using protocol-specified 1-sided log-rank test significance level of 0.1), assuming 140 events & 2 years of follow-up from randomization. However, further accrual to E2906 was suspended in 2/2015 by independent DSMC due to superior OS observed with standard Arm, so that 'Step 3' completed only 70% of target accrual. P-values reported are two-sided by convention unless specified otherwise. Results: 'Step 3' total accrual was n=120 (of 172 planned) (DAC 61, OBS 59), with median age 69 yrs (range 60-85), and groups were very well balanced for baseline clinical characteristics; most pts had Intermediate risk cytogenetics (74.2%) and ECOG performance status (PS)=0/1 (96%). The median number of DAC cycles received was 6 (range 0-13), and analysis was 'intention-to-treat'. The median follow-up is 49.8 months. There were 90 DFS events (47 OBS, 43 DAC), with 82 deaths (46 OBS, 36 DAC). Univariate DFS and OS are shown in Figure, with associated two-sided p-values; using protocol-prespecified one-sided significance level of 0.1, OS was significant (one-sided p=0.06) for DAC v. OBS, and there was a statistical trend favoring DFS (one-sided p=0.11), particularly for CLO pts (Table). We also performed multivariate Cox model (after adjustment for ECOG PS, sex, secondary AML, and baseline hematologic parameters) which confirmed superior HR for DFS (one-sided p=0.10) & OS (one-sided p=0.07), per statistical design. FLT3-ITD status is available for n=96 pts, and 84 were FLT3-ITD-negative (46 OBS, 38 DAC). Importantly, we observed a significant association of DAC maintenance with superior OS in the large FLT3-ITD-neg subgroup (p=0.039) (Figure). DAC was generally well tolerated apart from grade 3 febrile neutropenia (9%) and reversible grade 4 cytopenias, with no grade 5 events. Conclusions: In this randomized phase II study, DAC maintenance for 1 year after intensive AML therapy was associated with improved HR for OS and a trend for DFS, using protocol-specified statistical design. Furthermore there was a significant impact on OS for the FLT3-ITD-negative population. We acknowledge limitations based on incomplete accrual due to early termination of the parent E2906 study, and inherent to the phase 2 design of this E2906 endpoint, but results suggest an important impact of DAC maintenance on survival. These data strongly support a definitive phase III randomized study of DAC maintenance, particularly focused on the large intermediate risk FLT3-ITD-negative subgroup. Disclosures Foran: Agios: Honoraria, Research Funding. Claxton:Daiichi Sankyo Co. and Ambit Biosciences Corp, Astellas Pharma, Novartis Pharmaceuticals, Incyte Corporation, Cyclacel Pharmaceuticals, Inc, Celegene Corporation, Medimmune, Inc, Merck Sharp & Dohme Corp., Gilead Sciences, Inc.: Research Funding. Lazarus:Pluristem Therapeutics, Inc: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Speakers Bureau; Genentech: Speakers Bureau; Biosight: Membership on an entity's Board of Directors or advisory committees; Actinium Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Honoraria, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau; Adaptive Biotechnologies: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria, Speakers Bureau; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AstraZeneca: Honoraria, Speakers Bureau; Teva Pharmaceuticals: Speakers Bureau; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; CSL Behring: Consultancy. Rowe:BioSight: Consultancy. Altman:Cancer Expert Now: Consultancy; Glycomimetics: Consultancy, Honoraria, Other: Data Safety and Monitoring Committee; prIME Oncology: Speakers Bureau; PeerView: Speakers Bureau; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Theradex: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; France Foundation: Speakers Bureau; Daiichi Sankyo: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Biosight: Other: US Lead. Luger:Ariad: Research Funding; Agios: Honoraria; Biosight: Research Funding; Seattle Genetics: Research Funding; Pfizer: Honoraria; Onconova: Research Funding; Kura: Research Funding; Jazz: Honoraria; Genetech: Research Funding; Daichi Sankyo: Honoraria; Cyslacel: Research Funding; Celgene: Research Funding. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding. Zheng:Pfizer: Research Funding. Pratz:AbbVie: Consultancy, Research Funding; Agios: Consultancy, Research Funding; Millenium/Takeda: Research Funding; Boston Biomedical: Consultancy; Astellas Pharma: Consultancy, Research Funding. Powell:Jazz Pharmaceuticals: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy, Research Funding; Janssen: Research Funding; Novartis: Consultancy, Speakers Bureau; Rafael Pharmaceuticals: Consultancy, Research Funding. Tallman:Tetraphase: Consultancy, Membership on an entity's Board of Directors or advisory committees; Nohla: Consultancy, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Rigel: Consultancy, Membership on an entity's Board of Directors or advisory committees; Delta Fly Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Biosight: Research Funding; KAHR: Consultancy, Membership on an entity's Board of Directors or advisory committees; Orsenix: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; BioLineRx: Consultancy, Membership on an entity's Board of Directors or advisory committees; ADC Therapeutics: Research Funding; UpToDate: Patents & Royalties; Cellerant: Research Funding; Daiichi-Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Oncolyze: Consultancy, Membership on an entity's Board of Directors or advisory committees. Off Label Disclosure: Use of maintenance Decitabine in AML

The prognosis of elderly patients (pts) with acute lymphoblastic leukemia (ALL) remains poor, and novel therapeutic approaches are clearly needed. CD19 is expressed on the majority of precursor-B ALLs and represents an attractive therapeutic target. The anti-CD19 bi-specific engager antibody blinatumomab has demonstrated significant activity in both relapsed/refractory ALL and minimal residual disease (MRD) positive ALL. Therefore, we evaluated blinatumomab as a single agent in the upfront treatment of newly diagnosed elderly pts with Philadelphia chromosome (Ph) negative B-lineage ALL to determine response rates and overall survival (OS). Methods: Pts were treated at National Clinical Trial Network sites from June 2015 to September 2017. The primary objective of the study was to estimate 3-year OS. An IND was approved by the FDA and the protocol was approved by a central institutional review board. Eligibility: age > 65 years, newly diagnosed Ph negative B-lineage ALL with adequate organ function and no evidence of central nervous system (CNS) disease. Pts received blinatumomab for induction at standard dosing for 1-2 cycles until attainment of complete response (CR) or CR with incomplete count recovery (CRi) (defined below). Pts then received 3 cycles of blinatumomab post-remission therapy followed by 18 months of maintenance POMP (prednisone, vincristine, 6-mercaptopurine, methotrexate). A total of 8 doses of intrathecal methotrexate were administered as CNS prophylaxis. Cytogenetic risk was ascribed by NCCN 2018 criteria and bone marrow samples were analyzed for the presence of the Ph-like signature. MRD was assessed centrally by 8 color flow cytometry pre-treatment, on Day 35 of induction cycle 1, and on Day 35 of re-induction (if applicable). Response was assessed at the completion of 1-2 cycles of blinatumomab. CR was defined as < 5% marrow blasts with no evidence of extramedullary disease and recovery of counts [absolute neutrophil count (ANC) > 1000/uL, platelets >100,000/uL]. CRi was defined the same as CR but ANC < 1000/ uL and/ or platelets ≤ 100,000/ uL. OS was measured from day of registration on trial until the date of death. Disease-free survival (DFS) was measured from the date the pt achieved CR/ CRi until relapse or death. Toxicities were graded according to NCI CTCAE version 4.0. Results: Of 31 pts enrolled, 29 were eligible. The median age was 75 years (range 66 - 84), 22 (76%) were male, median baseline white blood count was 3.7 x 103/uL (range 0.3 - 7,100), and median bone marrow blast count percentage was 86.5% (range 30-100). Three pts received hydroxyurea or steroids prior to treatment initiation. Cytogenetic risk at diagnosis was: poor (34% of pts; n=10), standard (55% of pts; n=16), good (3% of pts; n=1) and unknown (7% of pts, n=2). Testing for the Ph-like signature is being completed. The most common Grade 3-5 non-hematologic toxicities related to treatment during induction were hyperglycemia (14%), dyspnea (10%), febrile neutropenia (10%), hypertension (10%), and lung infection (7%). One pt developed Grade 3 cytokine release syndrome and 1 developed Grade 3 neurotoxicity. No pts died during the first 28 days of treatment. The overall response rate (CR + CRi) was 66% (all CRs). Thirteen of the 19 responders have available MRD data post-treatment. Of these, 12 pts (92%) achieved MRD negativity, all at Cycle 1 Day 35. One pt required 2 cycles of blinatumomab to achieve CR. One pt proceeded to allogeneic hematopoietic stem cell transplant. The median follow-up time is 1 year and median duration on trial is 170 days (6 pts are still on maintenance therapy). OS estimated by Kaplan Meier at 6 months is 79% (95% CI 58%-90%) and at 1 year is 65% (95% CI 43%-80%). DFS estimated at 6 months is 68% (95% CI 43%-84%) and at 1 year is 56% (95% CI 31%-75%). No baseline features including CD19 expression (by percentage or mean-fluorescent intensity) or presence of a CD19 negative subpopulation were associated with response. Conclusions: Blinatumomab was well tolerated and effective in the treatment of newly diagnosed elderly patients with Ph negative B-lineage ALL. Further follow up will determine the durability of these responses. Disclosures Advani: Pfizer: Honoraria, Research Funding; Amgen: Research Funding; Novartis: Consultancy; Glycomimetics: Consultancy. Wieduwilt:Leadiant: Research Funding; Merck: Research Funding; Shire: Research Funding; Reata Pharmaceuticals: Equity Ownership; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding. Park:Adaptive Biotechnologies: Consultancy; Pfizer: Consultancy; AstraZeneca: Consultancy; Novartis: Consultancy; Kite Pharma: Consultancy; Juno Therapeutics: Consultancy, Research Funding; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Shire: Consultancy. Stock:Jazz Pharmaceuticals: Consultancy. Erba:Immunogen: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Agios: Consultancy, Speakers Bureau; Takeda/Millenium: Research Funding; Amgen: Research Funding; Novartis: Consultancy, Speakers Bureau; Juno: Research Funding; Juno: Research Funding; Celgene: Consultancy, Speakers Bureau; Daiichi Sankyo: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Glycomimetics: Consultancy, Other: Chair, Data and Safety Monitoring Committee; Takeda/Millenium: Research Funding; Incyte: Consultancy, Speakers Bureau; MacroGenics: Consultancy; Jazz: Consultancy, Speakers Bureau; MacroGenics: Consultancy; Agios: Consultancy, Speakers Bureau; Immunogen: Consultancy, Research Funding; Amgen: Research Funding; Agios: Consultancy, Speakers Bureau; Astellas: Research Funding; MacroGenics: Consultancy; Takeda/Millenium: Research Funding; Seattle Genetics: Consultancy, Research Funding; MacroGenics: Consultancy; Novartis: Consultancy, Speakers Bureau; Amgen: Research Funding; Novartis: Consultancy, Speakers Bureau; Janssen: Research Funding; Celgene: Consultancy, Speakers Bureau; Immunogen: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Janssen: Research Funding; Jazz: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Incyte: Consultancy, Speakers Bureau; Amgen: Research Funding; Glycomimetics: Consultancy, Other: Chair, Data and Safety Monitoring Committee; Pfizer: Consultancy, Other: grant; Glycomimetics: Consultancy, Other: Chair, Data and Safety Monitoring Committee; Astellas: Research Funding; Pfizer: Consultancy, Other: grant; Celgene: Consultancy, Speakers Bureau; Seattle Genetics: Consultancy, Research Funding; Incyte: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Agios: Consultancy, Speakers Bureau; Pfizer: Consultancy, Other: grant; Incyte: Consultancy, Speakers Bureau; Juno: Research Funding; Jazz: Consultancy, Speakers Bureau; Pfizer: Consultancy, Other: grant; Astellas: Research Funding; Seattle Genetics: Consultancy, Research Funding; Takeda/Millenium: Research Funding; Immunogen: Consultancy, Research Funding; Glycomimetics: Consultancy, Other: Chair, Data and Safety Monitoring Committee; Juno: Research Funding; Jazz: Consultancy, Speakers Bureau.

Background: The persistence of detectable MRD in complete remission (CR/CRi - CR with incomplete CBC recovery) has been reported to contribute to inferior outcome in younger AML patients (pts) in retrospective studies, however MRD has not been studied prospectively in older adults (age ≥60 yrs) receiving intensive therapy with curative intent. We performed a planned prospective study of MRD status after AML induction therapy in older adults, integrated into the large multicenter ECOG-ACRIN (E-A) E2906 Phase III trial. Methods Eligible patients age ≥60 yrs with AML were randomized 1:1 to receive either 'Standard' 7&3 (Dauno 60mg/m2) induction, with 2 cycles of intermediate dose Ara-C (1.5g/m2 x 12 doses; 6 doses if age ≥70) consolidation (Arm A); or single agent clofarabine (CLO) induction and consolidation (2 cycles) (Arm B). The design and primary clinical results for E2906 (n=727) have been reported previously (Foran et al, ASH #217a, 2015), demonstrating superior overall survival (OS) with standard therapy despite similar CR/CRi rates using stringent criteria, and similar 30-day induction mortality rates. Submission of diagnostic & remission bone marrow or peripheral blood samples was protocol mandated for prospective MRD assessment, and analysis was performed in the central E-A Leukemia Translational Research Lab (LTL) using 6-color multiparameter flow cytometry. MRD-positive (MRD+) was defined as ≥0.1%. LTL flow cytometric analysis was done blinded to treatment arm and outcome of patients. Only pt samples collected within +/-6 days of CR/CRi confirmation were included in this analysis. Statistical analysis was performed using X2 (categories) and Wilcoxon rank sum (continuous) tests to compare baseline patient and disease characteristics. Log-rank tests and multivariate Cox models stratified by treatment arm and adjusted for patient and disease variable (including WBC, cytogenetics, sex, performance status, secondary AML) were used to examine the MRD effect on OS and disease-free survival (DFS, relapse or death). Results The median follow-up is 47.8 months, and 297 of 685 evaluable patients (43.4%) achieved CR/CRi (Standard 44.6%; CLO 42.0%, p=ns). Remission MRD samples were only available for 147 CR/CRi patients (49.5%), owing to variability in sample viability and AML involvement, collection practices and timing of sample collection at individual sites, and patient/physician decision. 58/147 evaluable CR/CRi patients achieved MRD-negative (MRD-) status (Standard 40.7%, CLO 47.9%, p=0.74). Women (56.9% vs. men 43.1%, p=0.003) were more likely to be MRD-, but there was no other significant difference in MRD status stratified by clinical or disease features. MRD+ status at CR/CRi was associated with significantly inferior OS (p=0.031, Figure 1) and also inferior overall DFS (p=0.02); this was most pronounced for DFS after CLO (Arm B, Figure 2) (p=0.005), but not Standard (Arm A) therapy (p=0.41). The impact of MRD+ was confirmed on multivariate analysis using Cox Model Fitting, for OS: OS for All MRD+ pts, HR 1.64 (95% CI 1.00-2.68) (p=0.05); OS for Standard (Arm A) MRD+ pts, HR 1.06 (95% CI 0.51-2.21) (p=0.87); and OS for CLO (Arm B) MRD+ pts, HR 2.30 (95% CI 1.05-5.06) (p=0.04). There was a similar impact for DFS on multivariate analysis using Cox Model Fitting: DFS for All MRD+ pts, HR 1.86 (95% CI 1.16-2.98) (p=0.01); DFS for Standard (Arm A) MRD+ pts, HR 1.15 (95% CI 0.60-2.19) (p=0.67); and DFS for CLO (Arm B) MRD+ pts, HR 3.45 (95% CI 1.47-8.09) (p=0.004). Post-remission therapy was not stratified by MRD in E2906, and 33% of MRD-evaluable pts underwent allogeneic transplantation (no difference in transplant rate for MRD+ vs. MRD-). Conclusions MRD+ ≥0.1% is common (60.5%) after induction therapy in older adults & is significantly associated with inferior OS and DFS in 1st CR/CRi. However we observed excellent outcomes for MRD- pts in first CR/CRi regardless of induction regimen or post-remission therapy used. MRD+ pts in CR/CRi who went on to receive CLO consolidation had significantly poorer outcomes than those who went on to receive intermediate dose Ara-C consolidation. This observation differs strikingly from younger AML, and suggests that intensified Ara-C may abrogate the adverse impact of MRD in older pts in CR. These results strongly support incorporation of centralized MRD at the time of remission into future studies to guide optimal post-remission strategies in older pts with AML. Disclosures Foran: Agios: Research Funding; Xencor, Inc.: Research Funding. Lazarus:Pluristem Ltd.: Consultancy. Altman:Bayer: Other: payment to the institution to conduct clinical trial work; Pfizer: Other: payment to the institution to conduct clinical trial work; Boeringer Ingelheim: Other: payment to the institution to conduct clinical trial work; Epizyme: Other: payment to the institution to conduct clinical trial work; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Immune Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Cyclacel: Other: payment to the institution to conduct clinical trial work; Incyte: Other: payment to the institution to conduct clinical trial work; GSK: Other: payment to the institution to conduct clinical trial work; Agios: Other: Payment to the institution to conduct the trial ; Astellas Pharma: Other; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: payment to the institution to conduct clinical trial work; BMS: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Ariad: Other: payment to the institution to conduct clinical trial work; FujiFilm: Other: payment to the institution to conduct clinical trial work; Genetech: Other: Payment to the institution to conduct clinical trial work; Celator: Other: payment to the institution to conduct clinical trial work. Al-Kali:Novartis: Research Funding. Pratz:Millenium/Takeda: Research Funding; Agios: Research Funding; AbbVie: Consultancy, Research Funding; Astellas: Consultancy, Research Funding; Boston Scientific: Consultancy. Powell:Rafael Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Tallman:ADC Therapeutics: Research Funding; BioSight: Other: Advisory board; Daiichi-Sankyo: Other: Advisory board; Orsenix: Other: Advisory board; AROG: Research Funding; AbbVie: Research Funding; Cellerant: Research Funding.

Introduction: Despite data supporting the safety and efficacy of treatment for many older adults with AML, Methods: We conducted semi-structured interviews with 13 community oncologists (9 states) and 9 patients aged ≥60 with AML at any stage of treatment to elicit potential factors that influence treatment decisions. Patients were recruited from the outpatient clinics in a single institution and oncologists were recruited via email using purposive samples (patients: based on treatment received and stage of treatment; oncologists: based on practice location). Interviews were audio-recorded and transcribed. We utilized directed content analysis and adapted the decision-making model introduced by Zafar et al. to serve as a framework for categorizing the factors at various levels. A codebook was provisionally developed. Using Atlas.ti, two investigators independently coded the initial transcripts and resolved any discrepancies through an iterative process. The coding scheme was subsequently applied to the rest of the transcripts by one coder. Results: Median age of the oncologists was 37 years (range 34-64); 62% were females, 92% were white, 38% had practiced more than 15 years, and 92% reported seeing Conclusions: Treatment decision-making for older patients with AML is complex and influenced by many factors at the patient, disease/treatment, physician, and organizational levels. Despite studies supporting the utility of objective fitness assessments, these were not commonly performed in the community due to several barriers. Our framework will be useful to guide a larger study to assess real-life treatment decision-making in the community settings. We also identified several barriers raised by community oncologists that could be targeted to allow incorporation of objective fitness assessments. Figure 1. Figure 1. Disclosures Liesveld: Onconova: Other: DSMB; Abbvie: Honoraria. Stock:Jazz Pharmaceuticals: Consultancy. Majhail:Anthem, Inc.: Consultancy; Atara: Honoraria; Incyte: Honoraria. Wildes:Janssen: Research Funding. Klepin:Genentech Inc: Consultancy.

Background: Although approximately half of adult patients with acute lymphoblastic leukemia (ALL) achieve long-term survival, those who relapse have poor long-term outcomes (El Fakih et al. Hematol Oncol Stem Cell Ther. 2017; Oriol et al. Haematologica. 2010). The initial report of Phase 1 of ZUMA-3, the Phase 1/2 trial of KTE-C19 for treatment of relapsed/refractory (R/R) ALL (NCT02614066), has thus far demonstrated promising efficacy among patients infused with KTE-C19, with a 71% complete remission (CR) rate (CR or CR with incomplete hematologic recovery [CRi]), 88% undetectable minimal residual disease (MRD), and manageable toxicity across all doses (Shah et al. ASH 2017. #888). Here, we present updated safety and efficacy data from Phase 1 of ZUMA-3. Methods: Adult patients (≥ 18 y) with R/R ALL (Ph+ allowed), > 5% bone marrow blasts, and ECOG 0-1 received 2, 1, or 0.5 × 106 CAR T cells/kg after low-dose conditioning chemotherapy with fludarabine 25 mg/m2/day for 3 days and a single dose of cyclophosphamide 900 mg/m2 on the third day of conditioning. The primary endpoint for Phase 1 was incidence of dose-limiting toxicities (DLTs). Key secondary endpoints included incidence and time to onset and resolution of adverse events (AEs), rate of undetectable MRD remission in the bone marrow using flow cytometry, and duration of remission. KTE-C19 expansion and persistence were also assessed. Safety analyses included all patients who received KTE-C19, and patients with ≥ 2 months of follow-up were evaluated for efficacy. Results: As of April 12, 2018, 35 patients have received KTE-C19 with a median follow-up of 11 months (range, 2 - 25 months). The median age was 40 years (range, 18 - 69 years), 51% of patients were male, 66% had ECOG 1, 13 patients (37%) had prior blinatumomab, and 60% had received ≥ 3 prior lines of treatment. The median bone marrow blast burden at screening was 70% (range, 5 - 100). Six patients received the 2 × 106 cells/kg dose, 14 received 1 × 106 cells/kg, and 15 received 0.5 × 106 cells/kg. No DLTs were observed in the DLT period. The most common Grade ≥ 3 AEs were hypotension (40%), pyrexia (34%), decreased platelet counts (34%), and anemia (31%). Grade ≥ 3 CRS occurred in 9 patients (26%), with a median time to onset of 5 days (range, 1 - 15 days). There were 2 KTE-C19-related Grade 5 events: 1 cerebral infarction at the 0.5 × 106 cells/kg dose and 1 previously reported multiorgan failure secondary to cytokine release syndrome (CRS) at the 2 × 106 cells/kg dose. Grade ≥ 3 CRS resolved in all patients (not including 2 patients with a Grade 5 event), and the median time to resolution was 11 days (range, 7 - 42 days). Grade ≥ 3 treatment-emergent neurologic events occurred in 16 patients (46%), and the median time to onset was 7 days (range, 4 - 24 days). With the exception of 2 patients with unresolved neurologic events due to death, Grade ≥ 3 neurologic events resolved in all patients (14/14), with a median time to resolution of 17 days (range, 6 - 53 days). Among the 32 patients evaluable for response, the overall rate of undetectable MRD was 78% (95% CI, 60% - 91%). CR or CRi was achieved by 23 patients (72%), and 1 patient (3%) had blast-free BM. KTE-C19 levels were examined in 23 patients as of July 31, 2017. Robust KTE-C19 expansion was observed across all dose levels assessed. Conclusion: High rates of remission were achieved by adult patients with R/R ALL, with approximately three-quarters of patients achieving CR or CRi with undetectable MRD after a single dose of KTE-C19 in ZUMA-3. The safety profile was generally manageable, and most cases of high-grade CRS and neurologic events resolved. These results demonstrate that KTE-C19 offers clinical benefit for patients with otherwise limited treatment options. Disclosures Wierda: AbbVie, Inc: Research Funding; Genentech: Research Funding. Bishop:United Healthcare: Employment; Seattle Genetics: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Speakers Bureau; Juneau Therapeutics: Speakers Bureau; Novartis Pharmaceuticals Corporation: Speakers Bureau. Logan:Adaptive Biotech: Consultancy; Napajen: Consultancy; Shire: Consultancy; Pfizer: Consultancy; Novartis: Consultancy, Research Funding; Incyte: Consultancy; Jazz Pharmaceuticals: Consultancy, Research Funding; Amgen: Consultancy; Astellas: Research Funding; Pharmacyclics: Research Funding; Kite: Research Funding. Schiller:Astellas Pharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; bluebird bio: Research Funding. Holmes:Unum: Research Funding; Seattle Genetics: Research Funding, Speakers Bureau; Novartis: Research Funding; Genentech: Research Funding; Celgene: Research Funding; Rigel: Consultancy; Gilead: Consultancy, Research Funding, Speakers Bureau; Bayer: Consultancy. Abedi:Seattle Genetics: Speakers Bureau; Celgene: Speakers Bureau; Amgen: Research Funding; CIRM: Research Funding; BMS: Speakers Bureau; Takeda: Speakers Bureau; Gilead: Speakers Bureau; Celgene: Research Funding. Arellano:Cephalon: Research Funding. Pagel:Pharmacyclics, an AbbVie Company: Consultancy; Gilead: Consultancy. Mardiros:Kite, a Gilead Company: Employment; Kite, a Gilead Company: Equity Ownership; Mustang Bio: Patents & Royalties; Kite, a Gilead Company: Other: TRAVEL, ACCOMMODATIONS, EXPENSES. Shen:Zhejiang DTRM Biopharma LLC: Other: Clinical Operations Director. Vezan:Kite Pharma: Employment; Kite, Gilead, Abbv, MRK: Equity Ownership. Jain:Kite Pharma, Amgen: Equity Ownership; Kite Pharma: Employment; Kite Pharma: Patents & Royalties.

Introduction: Hematopoietic cell transplantation (HCT) advances in reduced intensity conditioning, donor identification, and supportive care have led to its increased use over the last few decades. HCT is a complex process that requires coordination at multiple levels, and there may be disparities in its utilization. To better understand these access disparities, we conducted a systematic review of studies that assessed barriers to referral and/or receipt of HCT. Additionally, we focused on a subgroup of older patients (aged ≥65 at transplant), who we hypothesized would be at higher risk for access barriers to HCT. Methods: A systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched for articles published in English from PubMed, Embase, Cumulative Index for Nursing and Allied Health, and Cochrane Central Register of Controlled Trials between the database inception and January 12th, 2018. Inclusion criteria were: 1) clinical trials, observational, qualitative, cross-sectional, or mixed-method study designs; 2) study assessed barriers to HCT or factors associated with referral for or receipt of HCT (except for country-specific economic factors as these are less likely to be targetable), 3) included patients ≥18 years with cancer. Narrative review articles and abstracts without full text were excluded. Two authors independently reviewed all titles and abstracts (N=3,262) and assessed studies for full-text eligibility (N=153). A third reviewer resolved any discrepancies. Eighteen studies met eligibility criteria and an additional 5 studies (not identified on our search strategy) were included on review of the bibliographies. Literature on subgroup of patients aged ≥65 was also assessed. Results: Among the 23 studies included, 16 were published after 2010. Studies were retrospective (N=18; 14 from registry data), cross-sectional (N=4; 2 from registry data), and mixed-method (N=1), and primarily conducted in the US (N=21). Barriers were assessed at the patient level (N=19; sample size ranged from 350 to 38,420), healthcare professional level (N=3; 1 study assessed both patients and healthcare professionals), or country level (N=2). Fourteen studies included some information on age of the patients and 10 studies included some patients aged 60 and above. Seventeen studies only included patients with hematologic malignancies. Age was the most common barrier identified (N=16 out of 16 studies identified older age as a barrier). Fourteen studies showed that older age was associated with lower odds of referral for or receipt of HCT, and the remaining 2 studies provided descriptive data showing lower percentages of patients receiving HCT compared to the younger age groups. Table 1 shows other potential barriers or factors associated with lower referral for or receipt of HCT at the patient, disease, physician, and organizational levels. These included race (N=14 out of 16 studies identified non-white race as a barrier), insurance or financial capacity (N=11/12), comorbidity (N=8/9), gender (N=7/17; primarily female), disease status (N=5/5), patient preferences (N=5/5), time of diagnosis (N=5/5), cancer type (N=4/6), and socioeconomic status (N=4/5). Only one study evaluated factors associated with receipt of HCT in a subgroup of patients ≥65 years. Older age, female gender, and a diagnosis of leukemia other than acute myeloid leukemia were associated with lower odds of receiving HCT. Conclusions: There are limited prospective studies evaluating access barriers to HCT in adult patients with cancer. Older age is the most commonly reported barrier to both autologous and allogeneic HCT, although studies have not addressed specific mechanisms for this disparity. In addition, other potential barriers identified such as gender, race, insurance status, and comorbidity have not been well studied in the context of older age. While some barriers may be difficult to intervene upon (e.g. comorbidity, disease status, performance status), many are amenable to interventions (e.g. socioeconomic status, distance to transplant center, social support). With the increasing trend for HCT in older patients, there is a critical need for prospective studies that better describe these access barriers and their mechanisms in order to design future interventions to reduce disparities in HCT access. Figure. Figure. Disclosures Liesveld: Onconova: Other: DSMB; Abbvie: Honoraria. Aljitawi:Medpace: Consultancy; The University of Rochester Medical Center: Patents & Royalties: Pending patent related to decellularized Wharton's jelly matrix. Klepin:Genentech Inc: Consultancy. Stock:Jazz Pharmaceuticals: Consultancy. Wildes:Janssen: Research Funding. Majhail:Incyte: Honoraria; Anthem, Inc.: Consultancy; Atara: Honoraria.

The prognosis of patients (pts) with relapsed/ refractory acute lymphoblastic leukemia (ALL) remains poor and novel therapies are needed. The anti-CD22 immunoconjugate inotuzumab ozogamicin (INO) has demonstrated promising results in both phase 2 and 3 trials (Kantarjian et al. Lancet Oncology 2012; 13(4): 403-11). Pre-clinical studies have demonstrated superior anti-tumor activity when INO is co-administered with cyclophosphamide (C), vincristine (V), and prednisone (P). In this study, SWOG 1312, we assess the safety of INO in combination with CVP and determine the maximum tolerated dose (MTD) of INO in this regimen for patients with relapsed or refractory (R/R) CD22+ acute leukemia (B-ALL, mixed phenotype, and Burkitts). Here, we present our toxicity results. Methods: Pts were treated at limited SWOG institutions from Apr 2014 to present. INO was supplied by Pfizer and an IND was approved by the FDA. The protocol was reviewed and approved by each institutional review board. Eligibility criteria included: age > 18 years (yrs), > 20% blasts expressing CD22, R/R CD22+ acute leukemia (B-ALL, mixed phenotype, or Burkitts), and adequate organ function. All pts received treatment with C (750 mg/m2) intravenous (IV) Day 1, V (1.4 mg/m2) (max 2 mg) IV Day 1, P (100 mg) orally Days 1-5 and IO (dose escalated as in Table 1) IV Days 1, 8, and 15. Each cycle was 28 days, and a maximum of 6 cycles could be administered. Dose escalation was performed using a standard 3x3 design; with the plan to treat 12 pts once the MTD was defined. Dose limiting toxicities (DLTs) were considered: (1) > Grade 4 non-hematologic toxicities with the exception of nausea, vomiting and toxicities secondary to neutropenia and sepsis; (2) prolonged myelosuppression [absolute neutrophil count (ANC) < 500/ uL or platelet count < 25,000/uL] in a bone marrow with < 5% blasts and no evidence of leukemia that lasts > 35 days beyond the most recent dose of IO; (3) any grade 3 non-hematologic toxicity (excluding peripheral neuropathy, hyperglycemia, and toxicities secondary to neutropenia, thrombocytopenia, and sepsis) that does not resolve to Grade 2 or better by 7 days beyond the most recent dose of IO; (4) any > Grade 3 elevation in SGOT/ SGPT or bilirubin lasting ≥ 7 days; (5) any IO-related toxicity resulting in permanent discontinuation of IO. Results: As of 7/14/2016, 24 pts have been enrolled: 2 pts were ineligible and 3 pts are currently receiving treatment and are not evaluable for toxicity. Of the 19 evaluable pts, the median age was 49 yrs (range 21-75), 10 (53%) were male, and the median WBC at registration was 9.4 K/uL (range 0.9-59.6). All pts had B-ALL. The median time from initial diagnosis to registration was 774 days. Five pts were in 1st relapse, 8 in 2nd relapse, 3 in 3rd relapse, 1 in 4th relapse, and 2 pts were primary refractory. Five pts had received prior allogeneic hematopoietic stem cell transplant (AHSCT); 7 pts had poor risk cytogenetics (Ph+, -7, +8, complex, or hypodiploid). One death occurred during treatment and was attributed to pneumonia. Grade 3-4 hematologic toxicity related to treatment was common: neutropenia (11 pts), thrombocytopenia (7 pts), and anemia (6 pts). Grade 3-4 non-hematologic toxicities were almost exclusively febrile neutropenia. One DLT occurred at Dose Level 3: prolonged myelosuppression. No cases of hepatic veno-occlusive disease (VOD) occurred during treatment, and 1 pt experienced Grade 3 alkaline phosphatase at Dose Level 1. Three pts proceeded to AHSCT after study treatment; 1 pt developed VOD post AHSCT however, this fully resolved. Currently, 3 pts have been enrolled to Dose Level 4. Conclusion: The combination of CVP/IO is well tolerated and only 1 significant hepatic event (which subsequently resolved) was observed despite a heavily pre-treated group of patients. Further toxicity results and dose escalation will be presented at the meeting. Response data will also be presented if enrollment is complete. Disclosures Advani: Pfizer: Consultancy, Research Funding. Othus:Glycomimetics: Consultancy; Celgene: Consultancy. Erba:Pfizer: Consultancy; Juno: Research Funding; Gylcomimetics: Other: DSMB; Agios: Research Funding; Millennium Pharmaceuticals, Inc.: Research Funding; Astellas: Research Funding; Agios: Research Funding; Juno: Research Funding; Daiichi Sankyo: Consultancy; Celator: Research Funding; Gylcomimetics: Other: DSMB; Pfizer: Consultancy; Millennium Pharmaceuticals, Inc.: Research Funding; Sunesis: Consultancy; Seattle Genetics: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Jannsen: Consultancy, Research Funding; Ariad: Consultancy; Novartis: Consultancy, Speakers Bureau; Celator: Research Funding; Incyte: Consultancy, DSMB, Speakers Bureau; Pfizer: Consultancy; Celgene: Consultancy, Speakers Bureau; Jannsen: Consultancy, Research Funding; Daiichi Sankyo: Consultancy; Sunesis: Consultancy; Gylcomimetics: Other: DSMB; Pfizer: Consultancy; Sunesis: Consultancy; Ariad: Consultancy; Celator: Research Funding; Jannsen: Consultancy, Research Funding; Millennium Pharmaceuticals, Inc.: Research Funding; Ariad: Consultancy; Astellas: Research Funding; Astellas: Research Funding; Celator: Research Funding; Agios: Research Funding; Agios: Research Funding; Juno: Research Funding; Millennium Pharmaceuticals, Inc.: Research Funding; Juno: Research Funding; Gylcomimetics: Other: DSMB; Astellas: Research Funding; Jannsen: Consultancy, Research Funding; Ariad: Consultancy.

Background: The results of the primary endpoint of the E2906 North American Intergroup phase 3 trial - demonstrating significantly inferior OS after single agent clofarabine versus standard intensive daunorubicin & cytarabine induction and consolidation - strongly support the use of intensive therapy for patients age ≥60 years with newly-diagnosed AML who are fit for treatment. This result was achieved despite similar CR rates (including CRi - CR with incomplete blood count recovery) and similar early (30- & 60-day) induction mortality between study arms, raising the question as to the importance of achieving CR as an endpoint. Therefore, we performed a follow-up analysis to address the factors that contribute to early mortality, the necessity for 2nd induction cycle to achieve CR, and to assess the survival impact of the quality of remission. Methods: E2906 design, study population and results for the primary objective were reported previously (ASH 2015, abstr. #217a). We performed this updated analysis to evaluate clinical risk factors for early mortality and re-induction, and to assess the impact of response quality on OS. Univariate comparisons were made with Fisher's exact test (category) and t-test (continuous variable), and logistic regression models were used to examine risk factors associated with early mortality, and with requiring a 2nd cycle of induction therapy. We performed a landmark analysis (beginning Day 60 after initiation of therapy) to determine the impact of response quality (CR/CRi, morphologic leukemia-free-state (MLFS), and treatment failure - i.e. residual/refractory AML) on OS. Survival comparisons were performed with log-rank test. Results: A total of n=727 patients were registered to E2906, the median age is 68 years (range 60-86) and the median follow-up of surviving patients is now 18.3 months. Adjusting for treatment, cytogenetic risk group, FAB subtype, WBC count, and secondary AML, increasing age (p=0.06) and performance status (PS) >1 (p=0.05) were associated with 30-day mortality and only PS >1 (p=0.06) with 60-day mortality. Treatment arm (p=0.003), adverse cytogenetic risk group (p=0.02), increasing age (p=0.03) and baseline WBC We next performed a landmark analysis (day 60, n=608 evaluable patients) to evaluate OS in relation to the quality of response (Table). We observed an advantage in achieving CR and CR/CRi, although the benefit of CRi diminished greatly after 12 months, and OS after MLFS appeared more similar to treatment failure (Figure, p Conclusion: This follow-up analysis confirms the importance of CR regardless of the number of cycles of induction therapy required to achieve remission, and identifies risk factors associated with early mortality and with requiring re-induction. At longer follow-up the OS after CRi appears to be inferior to true CR, particularly after clofarabine. We hypothesize that this may be due to higher rates of minimal residual disease in CRi, and studies to determine this are being performed. MLFS is not associated with a better overall survival than frank treatment failure (i.e. residual disease) and therefore its value as a response category is uncertain. These results highlight the role of standard intensive remission induction therapy with the intent of achieving CR, which remains the standard of care for fit older adults. Table. Table. Figure 1. Figure 1. Disclosures Foran: karyopharm: Honoraria; novartis: Honoraria; medscape: Honoraria; Millennium Pharmaceuticals, Inc.: Research Funding; pfizer: Honoraria; boehringer ingelheim: Research Funding; agios: Research Funding; Cellerant: Research Funding. Melnick:Janssen: Research Funding. Altman:Novartis: Honoraria; BMS: Honoraria; Janssen: Honoraria; Syros: Honoraria. Al-Kali:Novartis: Research Funding; Celgene: Research Funding.

Background Acute Myelogenous Leukemia (AML) evolves as many patients who are responsive to therapy upfront are resistant to the same agents when applied at relapse. We previously reported the results of our prospective efforts to formally assess the evolution of the leukemia stem cell (LSC) population(s) during patients' clinical courses. We identified a 9-90 fold increase in LSC activity and greatly increased phenotypic diversity of the LSC population. To identify the potential mechanisms underlying these changes we further characterized functionally-defined LSC populations from paired diagnosis and relapse samples. Methods Primary bone marrow and peripheral blood samples were collected on IRB approved protocols from patients with newly diagnosed AML undergoing induction therapy as well as normal donors. Twenty-five patients who relapsed after achieving a complete remission were selected for further study. Screening studies identified seven patients whose pre-therapy samples demonstrated sustained engraftment of NSG mice following transplantation. Transcriptional profiling of highly enriched LSC populations from seven patients was performed using ABI TaqMan® Low Density Array (TLDA) qPCR analyses following pre-amplification using a novel 153 gene expression platform. Protein expression levels of interleukin-1 receptor accessory protein (IL1RAP) on bulk leukemia cells and LSC populations from 25 patients were assessed by flow cytometry. The impact of loss of IL1RAP was assessed using lentiviral based shRNA targeting all IL1RAP isoforms followed by assessment of proliferation, apoptosis, colony forming unit (CFU) activity and NSG engraftment capacity in human cell lines as well as in primary patient samples. Downstream signaling events for IL1RAP were probed using a small molecule inhibitor approach. Results While the majority of the LSC populations' gene expression profile remained stable, twelve genes were differentially expressed between pre-treatment and relapsed LSC populations including IL1RAP. Flow cytometric analyses confirmed that IL1RAP is overexpressed on both bulk leukemia populations as well as LSC populations at diagnosis and relapse in comparison to normal hematopoietic stem cell (HSC) populations. Targeting ILRAP1 using shRNA in both cell lines and primary AML samples resulted in impaired proliferation, increased apoptosis, a marked loss of CFU capacity and impaired NSG engraftment. IL1 signaling is known to involve both the MAPkinase and NFKappB pathways. To determine which pathways are involved in IL1RAP mediated LSC survival, we performed a small molecule inhibitor screen targeting elements in both signaling cascades. Established inhibitors of the NFKappaB pathway resulted in loss in loss of leukemic cell function while MAPK signaling inhibition had minimal to no effect. Conclusions We identified IL1RAP as being overexpressed in both bulk leukemia and functionally defined LSC populations from pre-treatment and relapsed AML samples. Loss of IL1RAP was associated with a marked decline in LSC function. Preliminary studies support a primary role for the NF Kappa B pathway in LSC function. Our findings support a critical role for IL1RAP in LSC function and support its development as a target for AML therapy in both the upfront and relapse setting. Disclosures Wang: Immunogen: Research Funding. Calvi:Fate Therapeutics: Patents & Royalties. Becker:Millenium: Research Funding.

Introduction: Acute Myeloid Leukemia (AML) patients who are refractory to induction chemotherapy (RF) have a dismal prognosis. Properties of AML cell populations that cause the refractory phenotype are poorly understood. It is postulated that the leukemia stem cell (LSC) pool promotes chemotherapy resistance in AML; yet whether differences exist in this pool as a function of eventual remission status, and thus may account for induction failure, is unknown. Our group has recently found that in AML patients who initially achieve complete remission (CR) and then relapse, the LSC pool evolves to become larger and more immunophenotypically diverse at the time of relapse [Blood 2013; 122(21): abstract #883]. Since relapsed AML patients are often refractory to salvage chemotherapy, we postulated that diagnostic specimens from RF AML patients would have enlarged, immunophenotypically-diverse LSC pools relative to AML patients achieving CR, implicating these properties in the refractory phenotype. Defining unique properties of LSCs in RF AML might provide greater insight into the mechanisms responsible for the treatment-resistant phenotype. Methods: RF AML patients were defined by having ≥ 6% leukemic blasts in their bone marrow or peripheral blood after 1 or 2 cycles of anthracycline/cytarabine-based induction chemotherapy. All studies were conducted with pre-treatment AML specimens on approved IRB protocols at the University of Rochester Medical Center. LSC frequency was determined by limiting dilution analysis and xenotransplantation into sublethally irradiated NOD scid gamma (NSG) mice. To determine immunophenotypically-defined cell populations harboring functional LSC activity, AML specimens were sorted into four distinct populations defined by CD34 and CD38 staining. The presence of LSC activity in the four resultant populations (CD34+/CD38-, CD34+/CD38+, CD34-/CD38+, and CD34-/CD38-) was determined by the ability of each sorted population to engraft NSG mice in primary and secondary transplantation experiments. RNA-seq analysis was conducted on LSC-enriched cell populations. Results: Specimens from RF AML patients were more likely to engraft NSG mice relative to those from AML patients achieving CR (6/6 vs. 13/29 in RF vs. CR patients, respectively; P=0.02). The LSC pool from six RF AML patients was studied in detail. LSC frequency ranged from 1/19 to 1/326,123. Four of the 6 RF specimens harbored LSC frequencies 6- to 7,700-fold higher than those previously reported in primary AML [Sarry et al. J Clin Invest 2011; 121(1384-395]. In 5/6 RF specimens, LSCs were present in more than one immunophenotypically-defined cell population. Relative to specimens from AML patients achieving CR, specimens from RF patients were more likely to harbor LSCs in both CD34+ and CD34- populations (P=0.04). Treatment of NSG mice xenografted with specimens from RF patients with anthracycline/cytarabine-based chemotherapy failed to eradicate disease from engrafted mice; thus, therapeutic outcome of NSG mice engrafted with specimens from RF patients resembles that seen in patients. To identify genes potentially driving the refractory LSC phenotype, we compared gene expression profiles of CD34+ cells from RF patients to those from AML patients achieving long-term remission and to those from normal donors. Ninety-nine genes were uniquely deregulated in RF LSCs, including numerous Homeobox transcription factors and components of the Wnt and Hedgehog signaling pathways, all implicated in the maintenance of stemness. Pathway analysis revealed that amino acid metabolic pathways critical to other treatment-resistant cancers and molecules involved in IL-1 signaling and implicated in metastasis of solid tumors are dysregulated in primary refractory LSCs. Conclusions: This study is the first to systematically analyze the LSC pool in primary refractory AML. Similar to our findings in relapsed AML, RF AML patients harbor enlarged, phenotypically diverse LSC pools relative to AML patients achieving CR. Challenge of leukemic mice with an anthracycline/cytarabine treatment regimen mimics the effect seen in patients, facilitating the development of patient-derived xenograft models of RF AML. We identify a refractory LSC gene signature, opening the door to future mechanistic investigations and novel therapeutic approaches for this AML patient population in great need. Disclosures Calvi: Fate Therapeutics: Patents & Royalties. Becker:Millenium: Research Funding.

[Graphic][1] Background: Induction therapy with daunorubicin (Dauno) & cytarabine (Ara-C) [DA] has been the standard of care for eligible older adults (age ≥ 60 years) with newly diagnosed acute myeloid leukemia (AML) for over 2 decades. Single agent Clofarabine (CLO) induction & consolidation (Consol.) therapy has demonstrated important clinical activity in this age group in large phase II studies. Lower induction mortality (IM) & similar reported complete remission rate (CR) & overall survival (OS), as well as notable activity in those with higher risk disease features [including unfavorable cytogenetics, therapy-related AML (t-AML) & prior antecedent hematologic disorder (AHD)] raises the possibility that a non-Ara-C-based regimen could achieve similar or superior OS with lower toxicity. Methods: We performed a randomized United States Intergroup Phase III trial of single agent CLO [30mg/m2 x 5 days induction; 20 mg/m2 re-induction (if indicated) & 2 cycles Consol.] vs. standard DA therapy [Dauno 60mg/m2 D1-3 & Ara-C 100mg/m2 D1-7 induction x 1-2 cycles; 2 cycles Consol. with Ara-C (1.5g/m2 Q12hrs D1-6 age 60-69; once daily if age 70+)] in patients (pts) age ≥ 60 yrs with newly diagnosed AML. Patients with serum creatinine >1.0 (or GFR 3 (PS>2 if age 70+ yrs) were excluded. Randomization was stratified by age (60-69 vs. 70+), t-AML, & AHD. Pts with HLA-matched donor were eligible for allogeneic transplantation (AlloHCT) after induction, and those completing Consol. were eligible for randomization #2 (R#2) to maintenance decitabine [20mg/m2 x 3D, monthly x 1 year] versus observation. With a target accrual of 747, E2906 was powered to determine non-inferiority [and possible superiority] of CLO vs. standard DA, and primary endpoint was OS. A weighted statistical analysis was performed to account for confounding impact of R#2. AlloHCT patients were censored at transplant in this analysis. Responses & cytogenetics were confirmed centrally and OS & CR rates were monitored by an independent Data Safety Monitoring Committee (DSMC) at pre-specified time points. Results: As of Feb 23, 2015, 727 pts were randomized. Median age was 68 years (range 60-86); 57% were male, and 38% were age ≥70 yrs. Treatment arms are well balanced for all baselineclinical & AML characteristics, & 30% had unfavorable cytogenetics. Of 659 with complete treatment information reported, 30.4% on DA vs. 40.1% on CLO received 2 cycles of induction (p=0.006). Median follow-up of surviving patients is 7.6 months. | | DA | CLO | p-value | | ------------------------------------- | ----- | ----- | ------- | | CR/CRi | 43.8% | 42.8% | p=0.87 | | 30-day mortality | 8.5% | 7.9% | p=0.89 | | 60-day mortality | 14.9% | 13.1% | p=0.58 | | Gr 4-5 Non-Heme Tox. Induction | 27% | 19% | p=0.02 | | Gr 4-5 Non-Heme Tox. Consol. | 20% | 7% | p=0.001 | Table 1. shows early treatment results (CR, toxicity) for the 686 pts randomized as of Dec 23, 2014 (2 months prior to study end, & excluding 90 with ongoing response evaluation). 374 pts have died (174, DA; 200, CLO) & significantly inferior OS was observed for CLO vs. DA \[Hazard Ratio (HR) 1.41 (95% CI 1.12-1.78)\] (Fig. 1). Planned subgroup analyses were performed (Table 2) demonstrating significant differences in OS after CLO for patients age 60-69 yrs, without AHD, & with intermediate risk cytogenetics; but not for those with Unfav. Cytogen. (Fig. 2) or t-AML. Based on the primary weighted analysis, DSMC recommended suspension of new accrual to E2906 on Feb 23, 2015 & all active patients on CLO were transitioned to DA Arm. | | N | HR CLO/Standard (95% CI) | | ----------------------- | --- | ------------------------ | | *Weighted OS | 727 | 1.41 (1.12-1.78) | | Unweighted OS | 727 | 1.23 (1.00-1.50) | | Age 60-69 | 449 | 1.48 (1.10-1.99) | | Age 70+ | 278 | 1.34 (0.93-1.93) | | Intermed. Risk Cytogen. | 378 | 1.77 (1.27-2.47) | | Unfav. Risk Cytogen. | 216 | 0.96 (0.65-1.43) | | No AHD | 604 | 1.46 (1.13-1.89) | | AHD | 123 | 1.22 (0.74-2.00) | | De novo AML | 627 | 1.52 (1.18-1.96) | | Therapy-related AML | 100 | 0.94 (0.54-1.61) | Table 2. Conclusions: Despite similar CR & IM, OS after single agent CLO is inferior to standard DA therapy for pts age ≥60 years with newly diagnosed AML who are fit for intensive therapy, and DA remains the standard of care. However no difference in OS was observed after CLO in some pre-specified high risk AML subgroups. R#2 & AlloHCT arms continue in E2906 for pts already enrolled. Embedded prospective minimal residual disease study at CR is being performed to identify pts at higher risk after CLO & DA. ![Figure 1.][2] Figure 1. Weighted Kaplan-Meier Curves for OS ![Figure 2.][2] Figure 2. Unfavorable Cytogenetics OS by Therapy Disclosures Off Label Use: Use of clofarabine in AML, and maintenance therapy with decitabine in AML. Claxton: Medimmune: Research Funding; BMS: Consultancy; Astellas: Research Funding; Cyclacel: Research Funding; Merck: Research Funding; Ambit: Research Funding. Levine: Loxo Oncology: Membership on an entity's Board of Directors or advisory committees; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees; Foundation Medicine: Consultancy. Altman: Seattle Genetics: Consultancy; BMS: Consultancy; Spectrum: Consultancy; Astellas: Consultancy; Ariad: Consultancy; Novartis: Consultancy. Al-Kali: Novartis: Research Funding. [1]: /embed/inline-graphic-2.gif [2]: pending:yes

Osteoprogenitor cells (OPCs) are marrow microenvironmental cells known to modulate hematopoietic stem and progenitor cells (HSPCs). Specifically, OPCs regulate HSPCs in response to Parathyroid hormone (PTH) treatment in murine models. However, the role of OPCs in human HSPC regulation and whether human OPCs can be manipulated is poorly understood. Niche stimulation is an appealing strategy to aid in the treatment of hematopoietic dysfunction. Myelodysplastic syndromes (MDS) are clonal disorders with ineffective hematopoiesis resulting in cytopenias and risk of transformation to acute leukemia (AML). In mouse models, disruption of the osteolineage cells can contribute to initiation of ineffective hematopoiesis with phenotypic features of MDS. Our long term goal is to utilize microenvironmental stimulation as a therapeutic tool to improve hematopoietic disorders. We hypothesized that human cells isolated from the marrow fraction containing spicules harbor HSPC supportive cells, which can be manipulated to improve HSPC support. Moreover we hypothesized that OPC number and function is impaired by dysplasia-initiated microenvironmental disruption as a potential mechanism for reduced support of HSPCs and ineffective hematopoiesis. Our objective was to isolate human bone marrow spicule associated cells (SACs) and define their ability to support HSPCs, determine the impact of PTH treatment of SAC/HSPCs interactions and characterize dysplasia-induced osteolineage changes in human MDS and AML bone marrow. To achieve this objective, we used normal as well as MDS/AML patient-derived OPCs using a mouse-human co-culture system. Human bone marrow SACs isolated by collagenase digestion were either used for co-culture, analyzed with flow cytometry or cultured in mineralization media in limited dilutions. To assess the potential impact of PTH on human OPC interaction with HSPCs, we developed a 7 day co-culture of human bone marrow SACs treated with either vehicle or PTH, with mouse Lineage- Sca1+ c-Kit+ (LSK) hematopoietic progenitor cells. At the end of the co-culture, all cells present were used for competitive transplantation. Transplant experiments demonstrated that PTH treatment of the human bone marrow SACs leads to improved function of the co-cultured LSK cells as demonstrated by significantly improved engraftment of the LSK cells after transplant into irradiated C57/bl6 recipient mice when sampled at pre-specified time points over a 20-week period (N=12, 2-way ANOVA; p < 0.05). Flow cytometry analysis showed that mature (Lin- CD31- CD146+ CD105-) and immature osteolineage (Lin- CD31- CD146+ CD105+) cells were present in SACs and more abundant compared to within BMMCs (1% vs 0.1% and 0.24% vs 0.12% for the same patient). Notably, the putative HSC-supportive MSC pool was increased in SACs vs BMMCs (0.052% vs 0.019%). The presence of OPCs was functionally confirmed using colony forming unit osteoblasts (CFU-OBs). CFU-OB frequency was calculated using L-Calc TM (StemCell technologies). Among normal donors the frequency of CFU-OBs was low in marrow donors >50 years old compared to These data demonstrate that human SACs contain HSPC-supportive cells which can be stimulated to improve HSPC function. Human SACs comprise MSCs and osteolineage cells including osteoprogenitor cells. Aging decreases OPC pools in SACs. Our data in our small sample also suggest that dysplastic bone marrow microenvironment may negatively impact OPCs, which may in turn decrease OPC support of HPSCs. PTH treatment in our in-vitro model shows the potential to improve the interaction between the OPCs and HSPCs, resulting in amelioration of HSC function. Together these data suggest a strategy where targeting the MDS microenvironment may add to the currently available treatment modalities. Disclosures Calvi: Fate Therapeutics: Patents & Royalties.

Abstract 3549 Introduction: Decitabine (5-aza-2'-deoxyctiidine) has demonstrated single agent activity in newly diagnosed acute myelogenous leukemia (AML). Complete response rates are low, however, and this agent has not been extensively studied in settings of relapsed or refractory disease where treatment responses are generally short in the absence of allogeneic stem cell transplantation. Most AML cases have activation of the mTOR pathway as evidenced by expression of phosphorylated p70S6 kinase or phopho-4EBP1. Since inhibitors of the mTOR pathway such as the tuberous sclerosis genes (TSC1 and TSC2) are hypermethylated in some cases of AML and there is evidence that decitabine may inhibit the PI3K/Akt pathway often activated after mTOR inhibition, we conducted a phase I study utilizing decitabine (DAC) followed by the mTOR inhibitor rapamycin in patients with relapsed/refractory AML to assess safety and feasibility. Methods: Patients ≥ 18 years of age with non-M3 AML with relapsed or refractory disease were eligible for this protocol. Patients who had relapsed after allogeneic stem cell transplant were eligible if they did not have active graft vs. host disease >grade 1 of skin. Patients received DAC 20 mg/m2 intravenously daily for 5 days followed by rapamycin from day 6 to 25 at doses of 2mg, 4mg, and 6 mg/day in a 3+3 dose escalation design. Cycles were 28 days in duration, and in the absence of overt progression of disease, patients could receive up to 6 cycles of therapy. A marrow aspirate was performed at day 5 to assess effects of single agent decitabine on mTOR and Akt pathway mediators. Bone marrow responses were assessed after cycles 1 and 3. Results: Thirteen patients were treated, and 12 are available for safety evaluation. The median age of patients is 64 years (range 46–78). Median marrow blast percentage at enrollment was 35% (range 6–83%). In the 2 mg dose cohort, 1 patient had disease progression before completion of cycle 1 and another patient in the first cohort had a history of prolonged neutropenia at the time of enrollment and experienced reversible grade 3 mucositis, which was deemed a DLT. Three more patients enrolled at this dose, and no further DLTs were observed, allowing dose escalation to the 4 mg and 6 mg cohorts. The MTD has not yet been reached. Reversible grade 2–3 mucositis occurred in 7 patients, but no other recurrent non-hematologic toxicities were seen. On the 2 mg cohort, all patients achieved therapeutic rapamycin levels (5–15 ng/ml) during the first cycle, and in 5/7 patients, the therapeutic level was achieved within 4 days of beginning rapamycin. In the 2 mg cohort, no cumulative increase in rapamycin levels occurred over subsequent cycles (4/7 completed >1 cycle). In the 4 mg cohort, one patient had an elevated level at day 9, and one patient on concomitant voriconazole had supra-therapeutic levels at day 16 and day 23. At the end of one cycle, 4 patients demonstrated disease progression, 5 had stable marrow blasts, and 4 demonstrated a decline in marrow blast percentage. Median survival to date is 6 months (range 1 to 15+ months). Two patients proceeded to allogeneic stem cell transplant, and one patient who relapsed shortly after stem cell transplant survived 4 months and demonstrated stable donor chimerism during that time. As assessed by Western blotting in 9 patients with evaluable samples at baseline, 87% of these cases expressed phospho (p)-4EBP1 at diagnosis, 56% p70S6K, 67% peIF4E, and 44% pAKT. In the 7 patients with Western blot samples evaluable at the end of cycle 1, 3 had decreases in p4EBP1 after the first cycle, and 4 had increased expression. Of the 7 evaluable patients, only 3 expressed baseline p70S6K, and this decreased in 2 and was unchanged in 1 patient. Conclusion: The combination of decitabine and rapamycin can be safely administered to patients with relapsed/refractory AML. Based on this phase I data, a phase II cohort to define efficacy can be conducted at the 2 mg rapamycin dosing given the therapeutic rapamycin levels demonstrated at this dose. Effects on mTOR mediators and on AKT can be serially assessed and are variable. Correlation with clinical response will require a phase II study. This trial is registered at clinical trials.gov as NCT00861874. Disclosures: Liesveld: Eisai: Research Funding, Speakers Bureau; Bristol-Myers Squibb: Speakers Bureau; Ariad: Honoraria. Off Label Use: This is a phase 1 study to see if rapamycin is safe in AML.

Abstract 3771 Poster Board III-707 High throughput screening of compounds comprising the Memorial Sloan Kettering chemical library resulted in several confirmed hits against the recombinant Cdc7:Dbf4 heterodimeric kinase, a key regulator in the initiation of DNA replication and the G1 to S phase transition. Chemoinformatic analysis of the hits revealed an enrichment in one chemical cluster made up of several naturally occurring compounds, of which the most potent compound, CKI-7, was selected for further investigation. First, CKI-7 was found to be a non competitive inhibitor for ATP and prompted us to prolife it against a panel of 200 known kinases in order to assess its selectivity profile. The results were as predicted and very few kinases were specifically affected. Second, CKI-7 cytotoxic activity was assessed against a panel of well established cancer cell lines representing both hematopoietic and solid tumor malignancies as well as against a panel of primary hematopoietic cells derived from leukemia patients (both chemotherapy naïve and relapsed/refractory samples) and was found to be a very effective agent with potencies in the low nanomolar range. Subsequent studies using an isogenic pair of cell lines with one over expressing the Bcl_xL anti-apoptotic protein further confirmed the induction of the intrinsic apoptotic pathway via caspase-3 activation in the absence and attenuation of the activity in the presence of Bcl_xL. This was further demonstrated through standard cell cycle synchronization studies revealing that exposure to the Cdc7 inhibitor results in an S phase arrest, cell cycle dependent caspase-3 activation, and apoptotic cell death. This cell death is the direct result of Cdc7 kinase inhibition by CKI-7 as demonstrated using a Cdc7 substrate biomarker assay. Third, the physicochemical properties of this class of naturally occurring compounds also prompted us to investigate their effect on several multidrug resistence (MDR) over-expressing cell lines. We found that CKI-7 was not a substrate for the efflux pumps demonstrating that this novel compound can overcome a major mechanism of chemotherapy resistence in human tumor cells. Based of the above observations, in vivo dose-dependent anti-tumor activity of CKI-7 was subsequently demonstrated in a SCID-Beige mouse systemic tumor model utilizing a recently isolated Philadelphia chromosome positive acute lymphoblastic leukemia cell line (PhALL3.1). Taken together, our data confirm that Cdc7 is a new promising target for cancer therapy, and that the newly discovered inhibitor CKI-7, a naturally occurring selective small molecule inhibitor of this enzyme, is an equally promising novel cancer therapeutic agent. Disclosures: No relevant conflicts of interest to declare.

Cdc7 is a heterodimeric serine/threonine protein kinase that is a key regulator in the process of initiation of DNA replication and the G1 to S phase transition. Both the kinase and its known substrates are over-expressed in the majority of human cancers. As a result of the recent progress in the areas of pharmacogenetics and high throughput screening technology, identifying specific small molecule inhibitors of cell cycle regulated protein kinases has provided a means not only to study these signal transduction pathways but also to identify potential novel therapeutic agents. To this end, we have developed an assay for Cdc7 kinase inhibitory activity using a highthroughput screening (HTS) approach, screening over 250,000 natural and synthetic small molecules. As a result, we have identified and confirmed seventeen compounds, representing nine different chemical scaffolds, with Cdc7 kinase inhibitory activity. Based on potency, we selected the lead compound (CKI-7) which was further characterized using kinase profiling, microarray experiments, and standard cell based cytotoxicity assays. These latter studies demonstrated that CKI-7 induced cytotoxicity of established leukemia and lymphoma cell lines in culture with inhibitory concentrations (IC50s) in the low nanomolar range. Significantly, CKI-7 likewise induced cytotoxicity of MDR1 overexpressing cell lines with similar IC50s, demonstrating that this novel compound can overcome a major mechanism of chemotherapy resistence in human tumor cells. We additonally demonstrate that CKI-7 induces cytotoxicity of patient-derived primary acute leukemia tumor cells (both chemotherapy naïve and relapsed/refractory samples) in vitro at similarly low nanomolar concentrations. In vivo dose-dependent anti-tumor activity of CKI-7 was subsequently demonstrated in a SCID-Beige mouse systemic tumor model utilzing a recently isolated Philadelphia chromosome positive acute lymphoblastic leukemia cell line (PhALL3.1). Standard cell cycle synchronization studies established that exposure to CKI-7 results in cell cycle dependent caspase 3 activation and apoptotic cell death. This cell death is the direct result of Cdc7 kinase inhibition by CKI-7 as demonstrated using a substrate biomarker assay. In conclusion, our data confirm that Cdc7 is a new promising target for cancer therapy, and that CKI-7, a selective small molecule inhibitor of this enzyme, is an equally promising novel cancer therapeutic agent.