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PURPOSE Mosunetuzumab is a bispecific antibody targeting CD20 and CD3 that redirects T cells to engage and eliminate malignant B cells and is being developed for relapsed or refractory (R/R) B-cell non-Hodgkin lymphomas (B-NHLs). METHODS This first-in-human trial (ClinicalTrials.gov identifier: NCT02500407 ) evaluated the safety and tolerability and efficacy of mosunetuzumab in patients with R/R B-NHL and established the recommended phase II dose. Data from dose escalation are presented. Single-agent mosunetuzumab was administered intravenously in 3-week cycles, at full dose in cycle 1 day 1 (group A) or with ascending (step-up) doses during cycle 1 on days 1, 8, and 15 (group B), for eight or 17 cycles on the basis of tumor response. RESULTS Two hundred thirty patients were enrolled. Doses up to 2.8 mg and 60 mg were assessed in groups A and B, respectively; maximum tolerated dose was not exceeded. In group B (n = 197), common adverse events (≥ 20% of patients) were neutropenia (28.4%), cytokine release syndrome (27.4%), hypophosphatemia (23.4%), fatigue (22.8%), and diarrhea (21.8%). Cytokine release syndrome was mostly low-grade (grade ≥ 3: 1.0%) and mainly confined to cycle 1. Across the doses investigated (group B), best overall response rates were 34.9% and 66.2% in patients with aggressive and indolent B-NHL, respectively, and complete response rates were 19.4% and 48.5%. Among patients with a complete response, the median duration of response was 22.8 months (95% CI, 7.6 to not estimable) and 20.4 (95% CI, 16 to not estimable) in patients with aggressive and indolent B-NHL, respectively. CONCLUSION Mosunetuzumab, administered with step-up dosing, has a manageable safety profile and induces durable complete responses in R/R B-NHL. The expansion stage of the study is ongoing at the dose level of 1/2/60/60/30 mg selected for further study.

Purpose:Somatic mutations in phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), which encodes the p110α catalytic subunit of PI3K, are found in multiple human cancers. While recurrent mutations in PIK3CA helical, regulatory, and kinase domains lead to constitutive PI3K pathway activation, other mutations remain uncharacterized. To further evaluate their clinical actionability, we designed a basket study for patients with PIK3CA-mutant cancers with the isoform-specific PI3K inhibitor taselisib.Patients and Methods:Patients were enrolled on the basis of local PIK3CA mutation testing into one of 11 histology-specific cohorts and treated with taselisib at 6 or 4 mg daily until progression. Tumor DNA from baseline and progression (when available) was sequenced using a next-generation sequencing panel. Exploratory analyses correlating genomic alterations with treatment outcomes were performed.Results:A total of 166 patients with PIK3CA-mutant cancers were enrolled. The confirmed response rate was 9%. Activity varied by tumor type and mutant allele, with confirmed responses observed in head and neck squamous (15.4%), cervical (10%), and other cancers, plus in tumors containing helical domain mutations. Genomic analyses identified mutations potentially associated with resistance to PI3K inhibition upfront (TP53 and PTEN) and postprogression through reactivation of the PI3K pathway (PTEN, STK11, and PIK3R1). Higher rates of dose modification occurred at higher doses of taselisib, indicating a narrow therapeutic index.Conclusions:Taselisib had limited activity in the tumor types tested and is no longer in development. This genome-driven study improves understanding of the activity, limitations, and resistance mechanisms of using PI3K inhibitors as monotherapy to target PIK3CA-mutant tumors.

Mosunetuzumab is a CD20 × CD3 T-cell-engaging bispecific monoclonal antibody that redirects T cells to eliminate malignant B cells. In a phase 1 study, mosunetuzumab was well tolerated and active in patients with relapsed or refractory B-cell lymphoma. We, therefore, aimed to evaluate the safety and anti-tumour activity of fixed-duration mosunetuzumab in patients with relapsed or refractory follicular lymphoma who had received two or more previous therapies.We conducted a single-arm, multicentre, phase 2 study at 49 centres in seven countries (Australia, Canada, Germany, South Korea, Spain, UK, and USA). All patients were aged 18 years or older with histologically confirmed follicular lymphoma (grade 1-3a) and an Eastern Cooperative Oncology Group performance status of 0-1. Patients had disease that was relapsed or refractory to two or more previous lines of treatment, including an anti-CD20 therapy and an alkylating agent. Intravenous mosunetuzumab was administered in 21-day cycles with cycle 1 step-up dosing: 1 mg on cycle 1 day 1, 2 mg on cycle 1 day 8, 60 mg on cycle 1 day 15 and cycle 2 day 1, and 30 mg on day 1 of cycle 3 and onwards. Patients with a complete response by investigator assessment using the International Harmonisation Project criteria completed treatment after cycle 8, whereas patients with a partial response or stable disease continued treatment for up to 17 cycles. The primary endpoint was independent review committee-assessed complete response rate (as best response) in all enrolled patients; the primary efficacy analysis compared the observed IRC-assessed complete response rate with a 14% historical control complete response rate in a similar patient population receiving the pan class I PI3K inhibitor copanlisib. Safety was assessed in all enrolled patients. This study is registered with ClinicalTrials.gov, number NCT02500407, and is ongoing.Between May 2, 2019, and Sept 25, 2020, we enrolled 90 patients. As of the data cutoff date (Aug 27, 2021), the median follow-up was 18·3 months (IQR 13·8-23·3). According to independent review committee assessment, a complete response was recorded in 54 patients (60·0% [95% CI 49·1-70·2]). The observed complete response rate was significantly higher than the historical control complete response rate with copanlisib of 14% (p0·0001), thereby meeting the primary study endpoint. Cytokine release syndrome was the most common adverse event (40 [44%] of 90 patients) and was predominantly grade 1 (23 [26%] of 90) and grade 2 (15 [17%]), and primarily confined to cycle 1. The most common grade 3-4 adverse events were neutropenia or neutrophil count decreased (24 [27%] of 90 patients), hypophosphataemia (15 [17%]), hyperglycaemia (seven [8%]), and anaemia (seven [8%]). Serious adverse events occurred in 42 (47%) of 90 patients. No treatment-related grade 5 (ie, fatal) adverse event occurred.Fixed-duration mosunetuzumab has a favourable safety profile and induces high rates of complete remissions, allowing potential administration as an outpatient regimen, in patients with relapsed or refractory follicular lymphoma and two or more previous therapies.F Hoffmann-La Roche and Genentech.

Sarit Assouline and Won Seog Kim contributed equally. Introduction: Follicular lymphoma (FL) is considered an indolent yet incurable disease characterized by recurrent relapses: disease-free intervals shorten, and refractoriness increases with each relapse. Patients (pts) with FL who have received at least two prior systemic therapies typically have a poor prognosis. This is particularly true for those who have progression of disease within 24 months of front-line treatment (POD24), or are refractory to multiple agent classes; such patients are left with limited treatment options. Mosunetuzumab is a full-length, fully humanized immunoglobulin G1 CD20/CD3 bispecific antibody that redirects T cells to engage and eliminate malignant B cells. GO29781 (NCT02500407) is an ongoing open-label, multicenter, Phase I/Ib, dose-escalation and expansion study evaluating the safety, efficacy and pharmacokinetics of mosunetuzumab in pts with relapsed/refractory (R/R) B-cell lymphoma. Here, we present updated clinical data from pts with R/R FL treated with mosunetuzumab after at least two prior systemic therapies. Methods: Data are presented from Group B, in which pts received intravenous mosunetuzumab monotherapy as step-up doses in Cycle 1 on Days 1 and 8 and the target dose administered on Day 15. Mosunetuzumab was given on Day 1 of each subsequent 21-day cycle for 8 cycles in pts with a complete response (CR), and up to 17 cycles in those with a partial response (PR) or stable disease (SD). Results: As of January 21, 2020, 62 pts with FL (with at least two prior systemic therapies), received mosunetuzumab at dose levels between 0.4/1.0/2.8mg and 1/2/13.5mg (Cycle 1 Day 1/8/15 dose levels). The median age was 59 (range 27-85) years, and median number of prior therapies was 3 (range 2-11). Thirty-three pts (53%) were refractory to both a prior anti-CD20 antibody and an alkylating agent (double refractory), 30 (48%) had POD24, and four (6%) had received prior chimeric antigen receptor T-cell (CAR-T) therapy. The overall response rate (ORR) was 68% (42/62), with 31 pts (50%) achieving CR (Figure). Consistent CR rates were observed in high-risk pt populations, including those with double refractory disease (18/33 [55%]), POD24 (16/30 [53%]), PI3Ki refractory (7/9 [78%]), and those who received prior CAR-T therapy (2/4 [50%]). With a median time on study of 14.4 months, 26 pts (62% of all responders; including 74% of pts who achieved CR) remained in remission at the data cut-off. The median duration of response (DOR) was 20.4 months (95% CI: 11.7 months, upper limit not reached) for all 42 responders. The median PFS was 11.8 months (95% CI: 7.3-21.9 months). Adverse events (AEs) were reported in 60 pts (97%); serious adverse events (SAE) were reported in 22 pts (35%). The most frequently reported (>10% of pts) grade (Gr) 3 or higher AEs included hypophosphatemia (23%; transient and clinically asymptomatic) and neutropenia (21%; with a low rate of febrile neutropenia [2%]). Overall, 14 pts (23%) experienced CRS; in four pts, CRS was classified as a SAE. CRS events were reversible, mostly of Gr 1 or 2 (Gr 1, n=11; Gr 2, n=2; Gr 3, n=1; Lee, et al. Blood 2014), and predominantly occurred during Cycle 1. No patient required tocilizumab, intensive care unit admission or use of vasopressors for CRS management. Neurologic AEs (NAEs; defined by any AEs reported as Preferred Terms in SOC Nervous System Disorders and SOC Psychiatric Disorders) were observed in 28 pts (45%); all were Gr 1 (n=18) or 2 (n=10). The most commonly reported NAEs were headache (24%), insomnia (15%) and dizziness (11%). No Gr ≥3 NAEs or serious NAEs were reported. Conclusions: Fixed-duration mosunetuzumab monotherapy results in high response rates and durable disease control with a tolerable safety profile in heavily pretreated patients with FL, including known high-risk subgroups. Updated pharmacodynamics and biomarker data will be presented at the meeting. Disclosures Assouline: BeiGene: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Takeda: Research Funding; Pfizer: Consultancy, Honoraria; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; AstraZeneca: Consultancy, Honoraria, Speakers Bureau. Kim:Mundipharma: Research Funding; Donga: Research Funding; Kyowa Kirn: Research Funding; Celltrion: Research Funding; JJ: Research Funding; Pfizer: Research Funding; F. Hoffmann-La Roche: Research Funding. Sehn:Genentech, Inc.: Consultancy, Honoraria, Research Funding; AstraZeneca: Consultancy, Honoraria; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Seattle Genetics: Consultancy, Honoraria; Teva: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria; Servier: Consultancy, Honoraria; Chugai: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Apobiologix: Consultancy, Honoraria; Acerta: Consultancy, Honoraria; Merck: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Kite: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria; Lundbeck: Consultancy, Honoraria; TG therapeutics: Consultancy, Honoraria; Verastem Oncology: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; MorphoSys: Consultancy, Honoraria. Schuster:AlloGene, AstraZeneca, BeiGene, Genentech, Inc./ F. Hoffmann-La Roche, Juno/Celgene, Loxo Oncology, Nordic Nanovector, Novartis, Tessa Therapeutics: Consultancy, Honoraria; Novartis, Genentech, Inc./ F. Hoffmann-La Roche: Research Funding. Cheah:Celgene, F. Hoffmann-La Roche, Abbvie, MSD: Research Funding; Celgene, F. Hoffmann-La Roche, MSD, Janssen, Gilead, Ascentage Pharma, Acerta, Loxo Oncology, TG therapeutics: Honoraria. Nastoupil:Karus Therapeutics: Research Funding; Gilead/KITE: Honoraria; TG Therapeutics: Honoraria, Research Funding; Merck: Research Funding; Novartis: Honoraria, Research Funding; Gamida Cell: Honoraria; Bayer: Honoraria; Pfizer: Honoraria, Research Funding; LAM Therapeutics: Research Funding; Janssen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Genentech, Inc.: Honoraria, Research Funding. Shadman:Fred Hutchinson / University of Washington: Current Employment; Abbvie, Genentech, Inc., AstraZeneca, Sound Biologics , Pharmacyclics, Verastem, ADC therapeutics, Beigene, Cellectar, BMS, Mophosys and Atara Biotherapeutics: Consultancy; Mustang Bio, Celgene, Pharmacyclics, Gilead, Genentech, Inc., Abbvie, TG therapeutics, Beigene, AstraZeneca, Sunesis: Research Funding. Yoon:Amgen: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Kyowahako Kirin: Research Funding; Janssen: Consultancy; F. Hoffmann-La Roche: Other: All authors received support for third-party writing assistance, furnished by Scott Battle, PhD, provided by F. Hoffmann-La Roche, Basel, Switzerland., Research Funding; YuhanPharma: Research Funding. Matasar:Daiichi Sankyo: Consultancy; IGM Biosciences: Research Funding; Immunovaccine Technologies: Honoraria, Research Funding; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Teva: Consultancy; Rocket Medical: Consultancy, Research Funding; Seattle Genetics: Consultancy, Honoraria, Research Funding; GlaxoSmithKline: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Pharmacyclics: Honoraria, Research Funding; Juno Therapeutics: Consultancy; Takeda: Consultancy, Honoraria; Genentech, Inc.: Consultancy, Honoraria, Research Funding; Merck: Consultancy; Bayer: Consultancy, Honoraria, Research Funding. Diefenbach:Trillium: Research Funding; Millenium/Takeda: Research Funding; Merck: Consultancy, Research Funding; MEI: Research Funding; LAM Therapeutics: Research Funding; Incyte: Research Funding; Genentech, Inc.: Consultancy, Research Funding; Denovo: Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding. Gregory:Janssen: Consultancy; F. Hoffmann-La Roche, Genentech, Inc., MSD, AbbVie, BeiGene, AstraZeneca, Celgene, BMS: Research Funding; F. Hoffmann-La Roche, Novartis, AbbVie: Speakers Bureau; F. Hoffmann-La Roche, Novartis, Sandoz, Gilead, AbbVie, MSD: Honoraria; F. Hoffmann-La Roche, Novartis, Sandoz, Gilead: Membership on an entity's Board of Directors or advisory committees. Bartlett:BMS/Celgene: Research Funding; Merck: Research Funding; Kite, a Gilead Company: Research Funding; Immune Design: Research Funding; Janssen: Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Millennium: Research Funding; Pharmacyclics: Research Funding; Seattle Genetics: Consultancy, Research Funding; Affimed Therapeutics: Research Funding; Autolus: Research Funding; Acerta: Consultancy; Roche/Genentech: Consultancy, Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; BTG: Consultancy; ADC Therapeutics: Consultancy; Forty Seven: Research Funding. Wei:Genentech, Inc.: Current Employment; F. Hoffmann-La Roche: Current equity holder in publicly-traded company. Doral:Genentech, Inc.: Current Employment; F. Hoffmann-La Roche: Current equity holder in publicly-traded company. Yin:Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company. Negricea:F. Hoffmann-La Roche: Current Employment. Li:F. Hoffmann-La Roche: Current Employment, Current equity holder in publicly-traded company; Genentech, Inc.: Current Employment. Penuel:Genentech, Inc./ F. Hoffmann-La Roche: Current Employment; F. Hoffmann-La Roche: Current equity holder in publicly-traded company. Huang:F. Hoffmann-La Roche: Current Employment. Budde:AstraZeneca: Speakers Bureau; Merck, Amgen, AstraZeneca, Mustang Therapeutics: Research Funding; F. Hoffmann-La Roche, Kite Pharma: Consultancy. OffLabel Disclosure: Mosunetuzumab (RG7828) is a full-length, fully humanized immunoglobulin G1 (IgG1) bispecific antibody targeting both CD3 (on the surface of T cells) and CD20 (on the surface of B cells). Mosunetuzumab redirects T cells to engage and eliminate malignant B cells. Mosunetuzumab is an investigational agent.

TPS7588 Background: Despite significant progress with first-line immunochemotherapy, most patients with follicular lymphoma (FL) will eventually relapse with increasing refractoriness and decreasing duration of response to subsequent therapy lines (Rivas-Delgado et al. 2019). Mosunetuzumab (M) is a CD20xCD3 bispecific antibody that engages and redirects T-cells to eliminate malignant B cells (Sun et al. 2015). In an ongoing, pivotal Phase I/II trial of M monotherapy, patients with relapsed/refractory (R/R) FL who have received ≥2 prior treatment lines achieve deep and durable responses (NCT02500407; Budde et al. ASH 2021). Preliminary data from a Phase Ib study have suggested favorable safety and promising activity of M in combination with lenalidomide (Len), a potent immunomodulatory agent that has shown additive/synergistic activity with an anti-CD20 antibody in R/R indolent lymphoma (Leonard et al. 2019), in patients with R/R FL who have received ≥1 prior therapy (NCT04246086; Morschhauser et al. ASH 2021). The chemotherapy-free M-Len combination may represent a promising outpatient therapy option for future management of patients with R/R FL. The randomized, multicenter Phase III study has been initiated. Methods: CELESTIMO (NCT04712097) is a randomized, multicenter, open-label Phase III study evaluating the efficacy and safety of M-Len versus rituximab plus Len (R-Len) in patients with previously treated R/R FL. Patients must have histologically documented CD20+ FL (Grades 1–3a) requiring systemic therapy and have received ≥1 prior line of systemic therapy. Patients are randomized (1:1) to receive M-Len (M intravenously [IV] on Days [D] 1, 8 and 15 of Cycle [C] 1 [21-day cycle] and D1 of C2–12 [28-day cycles], plus Len orally [PO] on D1–21 of C2–12) or R-Len (R IV on D1, 8, 15 and 22 of C1 then on D1 of C3, 5, 7, 9, and 11, plus Len PO on D1–21 of C1–12 [all 28-day cycles]), and stratified by disease progression within 24 months of initial treatment (yes/no), number of prior lines of therapy (1 versus ≥2), and refractoriness to anti-CD20 therapy (refractory/non-refractory). The primary endpoint is progression-free survival (PFS) assessed by independent review committee; secondary endpoints include investigator-assessed PFS, complete and objective response, overall survival, and safety. Biomarkers predictive of response to M-Len and R-Len will also be investigated as exploratory endpoints. The study started recruitment in 2021 and plans to enroll ̃400 patients from approximately 16 countries and 150 sites globally. Clinical trial information: NCT04712097.

7526 Background: Mosunetuzumab (M) is a bispecific antibody targeting CD20 and CD3 that redirects T cells to engage and eliminate malignant B cells being developed for relapsed or refractory (R/R) B-cell non-Hodgkin lymphomas (B-NHL). CD20 is an optimal target, with uniform expression across B-NHL histologies and minimal receptor turnover. We characterized CD20 loss as a potential mechanism of resistance to M in patients (pts) on a Phase I/II trial (NCT02500407) receiving M monotherapy for the treatment (tx) of R/R B-NHL. Methods: Pts with R/R B-NHL received M intravenously in 3-week cycles, for eight to 17 cycles depending on tumor response. At baseline (BL), biomarker-evaluable (archival or fresh) biopsies were collected from 293 pts. Biopsies from 62 pts were collected at additional time points during tx with M and/or at disease progression (PD). The proportion of CD20+ and PAX5+ tumor cells was determined by immunohistochemistry (IHC) using dual-staining with anti-CD20 (clone L26, VENTANA) and anti-PAX5 (clone DAK-PAX5, DAKO) antibodies. Expression of MS4A1, the gene encoding CD20 , was measured by RNA-sequencing (RNA-seq); MS4A1 mutation profiling was performed by whole exome sequencing (WES). Levels of CD20 expression were assessed relative to response rates. Correlative analyses were performed and assessed centrally (IHC, RNA-seq, and WES) and locally (IHC). Results: CD20 levels were consistently high ( > 75% CD20+PAX5+ cells) in the majority of BL biopsies and generally comparable across histologies (FL, DLBCL, tFL, MCL, and RT). BL CD20 loss (≤5% CD20+PAX5+ cells) was seen in 16/293 pts (5.5%), more commonly in aggressive NHL, and responses to M were not seen in these pts. Among 62 pts with BL and on-tx/at-PD biopsies, BL CD20 levels were ≤5% in 7/62 pts (11%) (6/7 pts [86%] progressed before completing Cycle 2). CD20 levels were maintained in on-tx biopsies from 23/24 pts (96%). At PD, biopsies showed CD20 loss in 7/26 pts (27%). For five pts with BL, on-tx and at-PD biopsies, all pts maintained CD20 while on-tx and 1/5 pts (20%) had CD20 loss at PD. There was no clear association between CD20 reduction and histology. Data from 185 BL biopsies showed generally concordant levels of CD20 gene and protein expression (r = 0.72). In 10/185 pts (5%), MS4A1 was expressed without detectable CD20 protein expression; DNA sequencing revealed novel mutations in MS4A1, including mutations leading to truncation of the protein. CD20 transmembrane and extra-cellular domain mutations were also observed but do not block CD20 expression. Conclusions: In pts with R/R B-NHL treated with M, low BL CD20 expression is associated with lack of response to M. During M tx, loss of tumor cell expression of CD20 is one mechanism of acquired resistance; however, CD20 expression is maintained in most pts with PD, implying alternative mechanisms for acquired M resistance. Clinical trial information: NCT02500407.

Context Follicular lymphoma (FL) often presents with recurrent relapses. Treatment options for patients (pts) with FL who have received ≥2 prior lines of therapy are limited, and prognosis is poor. The safety and efficacy of mosunetuzumab, a full-length, fully humanized IgG1 CD20/CD3 bispecific antibody is currently being investigated in an ongoing open-label, multicenter, Phase I/Ib, dose-escalation and expansion trial in relapsed/refractory (R/R) B-cell lymphoma (GO29781; NCT02500407). Objective To present updated data from the R/R FL cohort. Methods Pts received intravenous mosunetuzumab step-up doses in cycle (C) 1, days (D) 1 and 8, then the target dose on D15 and D1 of each subsequent 21-day cycle (Group B); treatment continued for ≤17 cycles. Results As of January 21, 2020, mosunetuzumab 0.4/1.0/2.8 mg to 1/2/13.5 mg (C1D1/8/15 dose levels) was given to 62 pts with FL who received ≥2 prior systemic therapies. Pts had a median age of 59 (27–85) years, median number of 3 (2–11) prior therapies; 33 pts (53%) were double refractory, 30 (48%) had progression of disease within 24 months of first-line treatment (POD24), and four (6%) received prior chimeric antigen receptor T-cell (CAR-T) therapy. Overall response rate (ORR) and CR rate were 68% and 50%, respectively. In high-risk pts, consistent CR rates were observed: 55% (18/33) in pts with double refractory disease, 53% (16/30) in pts who had POD24, 78% (7/9) in pts with PI3Ki refractory FL, and 50% (2/4) in those who received prior CAR-T therapy. Twenty-six pts with a CR (74%) remained in remission (median time on study: 14.4 months). In responders (n=42), median duration of response was 20.4 months (95% CI: 11.7–not reached), and median progression-free survival was 11.8 months (95% CI: 7.3–21.9). Adverse events (AEs) and serious AEs were reported in 60 (97%) and 22 pts (35%), respectively. The most common grade (Gr) ≥3 AEs included hypophosphatemia (23%) and neutropenia (21%). Fourteen pts (23%) experienced CRS1; events were mostly Gr 1 or 2, reversible, and occurred largely during C1. Conclusions A high CR rate, durable responses, and a manageable safety profile were observed with mosunetuzumab monotherapy in heavily pre-treated pts with FL, including high-risk pts.

Dasatinib is a multi-tyrosine kinase inhibitor approved for treatment of Ph+ acute lymphoblastic leukemia (ALL), but its efficacy is limited by resistance. Recent preclinical studies suggest that dasatinib may be a candidate therapy in additional ALL subtypes including pre-BCR+ ALL. Here we utilized shRNA library screening and global transcriptomic analysis to identify several novel genes and pathways that may enhance dasatinib efficacy or mitigate potential resistance in human pre-BCR+ ALL. Depletion of the transcriptional coactivator CBP increased dasatinib sensitivity by downregulating transcription of the pre-BCR signaling pathway previously associated with dasatinib sensitivity. Acquired resistance was due, in part, to upregulation of alternative pathways including WNT through a mechanism, suggesting transcriptional plasticity. Small molecules that disrupt CBP interactions with the CREB KID domain or β-catenin showed promising preclinical efficacy in combination with dasatinib. These findings highlight novel modulators of sensitivity to targeted therapies in human pre-BCR+ ALL, which can be reversed by small-molecule inhibitors. They also identify promising therapeutic approaches to ameliorate dasatinib sensitivity and prevent resistance in ALL. Significance: These findings reveal mechanisms that modulate sensitivity to dasatinib and suggest therapeutic strategies to improve the outcome of patients with acute lymphoblastic leukemia. Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/22/6497/F1.large.jpg. Cancer Res; 78(22); 6497–508. ©2018 AACR.

Purpose: This single-arm, open-label phase II study evaluated the safety and efficacy of taselisib (GDC-0032) plus fulvestrant in postmenopausal women with locally advanced or metastatic HER2-negative, hormone receptor (HR)-positive breast cancer.Patients and Methods: Patients received 6-mg oral taselisib capsules daily plus intramuscular fulvestrant (500 mg) until disease progression or unacceptable toxicity. Tumor tissue (if available) was centrally evaluated for PIK3CA mutations. Adverse events (AE) were recorded using NCI-CTCAE v4.0. Tumor response was investigator-determined using RECIST v1.1.Results: Median treatment duration was 4.6 (range: 0.9–40.5) months. All patients experienced ≥1 AE, 30 (50.0%) had grade ≥3 AEs, and 19 (31.7%) experienced 35 serious AEs. Forty-seven of 60 patients had evaluable tissue for central PIK3CA mutation testing [20 had mutations, 27 had no mutation detected (MND)]. In patients with baseline measurable disease, clinical activity was observed in tumors with PIK3CA mutations [best confirmed response rate: 38.5% (5/13; 95% CI, 13.9–68.4); clinical benefit rate (CBR): 38.5% (5/13; 95% CI, 13.9–68.4)], PIK3CA-MND [best confirmed response rate: 14.3% (3/21; 95% CI, 3.0–36.3); CBR: 23.8% (5/21; 95% CI, 8.2–47.2)], and unknown PIK3CA mutation status [best confirmed response rate: 20.0% (2/10; 95% CI, 2.5–55.6); CBR: 30.0% (3/10; 95% CI, 6.7–65.2)].Conclusions: Taselisib plus fulvestrant had clinical activity irrespective of PIK3CA mutation status, with numerically higher objective response rate and CBR in patients with PIK3CA-mutated (vs. -MND) locally advanced or metastatic HER2-negative, HR-positive breast cancer. No new safety signals were reported. A confirmatory phase III trial is ongoing. Clin Cancer Res; 24(18); 4380–7. ©2018 AACR.

Background: Patients (pts) with relapsed/refractory (R/R) follicular lymphoma (FL) remain an unmet need population. Monotherapy with mosunetuzumab (M), a CD20xCD3 bispecific antibody, has demonstrated high and consistent response rates in high-risk R/R FL subsets, with early evidence of response durability and a favorable benefit/risk profile (Assouline et al. ASH 2020). Lenalidomide (Len) is clinically active in pts with FL, and its potent immunomodulatory activity offers the potential for additive/synergistic efficacy when combined with M. Here, we present initial data from an ongoing Phase Ib study (NCT04246086) evaluating the safety and activity of M+Len in R/R FL pts who have received at least one prior line of therapy. Methods: Pts with R/R FL (Grade [Gr] 1-3a) and at least one prior systemic anti-cancer therapy were enrolled to receive 12 cycles of M+Len (cycle duration: Cycle [C] 1, 21 days; C2-12, 28 days). In C1, step-up doses of M (IV infusion) are given on C1 Day (D)1 (1mg) and C1D8 (2mg), with the target dose given on C1D15 (30mg) and on D1 of C2-12. Len (20mg orally) is administered on D1-21 of C2-12. No hospitalization is mandated by the protocol. The primary objective is to evaluate the safety of M+Len; secondary objectives include assessment of response and long-term efficacy outcomes. Cytokine release syndrome (CRS) is reported using ASTCT criteria (Lee et al. Biol Blood Marrow Transplant 2019). Responses are assessed by investigators with PET-CT using Lugano 2014 criteria (Cheson et al. J Clin Oncol 2014). Results: At data cut-off (May 31, 2021), 27 pts had been enrolled. Median age was 59 years (range: 31-79 years); 12 pts (44%) were male. All pts had an ECOG performance status of 0 (18 pts, 67%) or 1 (9 pts, 33%). Median number of prior lines of therapy was 1 (range: 1-4), and 3 pts (11%) had disease progression (PD) 9 months. All 27 pts were safety evaluable at data cut-off. Twenty pts (74%) experienced ≥1 adverse event (AE) of any Gr; the most common AE was CRS (8 pts, 30%). Gr 3-4 AEs occurred in 8 pts (30%) and serious AEs in 8 pts (30%). No Gr 5 (fatal) AEs were observed. AEs relating to M occurred in 20 pts (74%) and AEs relating to Len occurred in 10 pts (37%). There were no AEs leading to withdrawal of M or Len; 2 pts had M-related AEs leading to M dose delays, 6 pts (22%) had Len-related AEs leading to Len dose interruption and/or reduction. In all pts, CRS events were Gr 1 (7/8 pts) or Gr 2 (1/8 pts). For most pts (6/8), CRS events occurred C1D1-C1D7; 2 pts experienced Gr 1 CRS events in C2. Median time to CRS onset was 1 day after first study drug administration (range: 1-28 days), median CRS duration was 3 days (range: 2-5 days). All CRS events resolved without sequelae. No pt required tocilizumab, ICU admission, high flow oxygen, or vasopressor support. Five pts (19%) reported 14 events of Gr 3-4 neutropenia; all neutropenia events occurred between D41 and D218, with a duration of 6-16 days. All neutropenia events resolved, with 1 patient receiving primary G-CSF prophylaxis and 2 pts receiving G-CSF treatment. No febrile neutropenia events occurred. The efficacy-evaluable population included all pts who had been assessed for response at any time on study, who had withdrawn from treatment or study prior to reaching their first response assessment, or who had been on study long enough to have reached their first scheduled response assessment, planned per protocol for D15-21 of C3. Objective response rate in the 13 pts who were efficacy evaluable at data cut-off was 92%, with complete metabolic response observed in 10 pts (77%), partial metabolic response (PMR) in 2 pts (15%), and stable disease in 1 patient (8%). One pt who initially achieved PMR experienced PD after 8 cycles of treatment. Conclusions: M+Len appears to have an acceptable safety profile in pts with R/R FL who have received at least one prior line of therapy, with encouraging preliminary anti-lymphoma activity observed. These data support initiation of a randomized Phase III study of M+Len versus rituximab+Len. Updated safety, efficacy, and pharmacokinetic data will be presented at the meeting. Disclosures Morschhauser: AstraZenenca: Membership on an entity's Board of Directors or advisory committees; Epizyme: Consultancy, Membership on an entity's Board of Directors or advisory committees; Chugai: Honoraria; Janssen: Honoraria; Genmab: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genentech, Inc.: Consultancy; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Roche: Consultancy, Speakers Bureau; Servier: Consultancy. Bishton: Nottingham University Hospitals NHS Trust: Current Employment; Celltrion: Honoraria; Tevapharma: Honoraria; Bristol-Myers Squibb: Honoraria; Gilead: Honoraria; F. Hoffmann-La Roche Ltd: Membership on an entity's Board of Directors or advisory committees. Eyre: Oxford University Hospitals NHS Foundation Trust: Current Employment; LOXO Oncology: Consultancy, Honoraria; Incyte: Consultancy, Honoraria; BeiGene: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Speakers Bureau; KITE/Gilead: Consultancy, Honoraria, Speakers Bureau; Secura Bio: Consultancy, Honoraria; AstraZeneca: Consultancy, Honoraria, Research Funding, Speakers Bureau. Bachy: Kite, a Gilead Company: Honoraria; Novartis: Honoraria; Daiishi: Research Funding; Roche: Consultancy; Takeda: Consultancy; Incyte: Consultancy. Cartron: Roche, Celgene-BMS: Consultancy; Danofi, Gilead, Novartis, Jansen, Roche, Celgene-BMS, Abbvie, Takeda: Honoraria. Ysebaert: AbbVie: Consultancy, Honoraria, Speakers Bureau; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; Gilead: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Speakers Bureau. Bobillo: F. Hoffmann-La Roche Ltd: Consultancy, Speakers Bureau; Gilead: Speakers Bureau. Budde: Kite Pharma: Consultancy; Genentech: Consultancy, Research Funding; AstraZeneca: Research Funding. Fox: F. Hoffmann-La Roche Ltd: Consultancy, Membership on an entity's Board of Directors or advisory committees. Knapp: F. Hoffmann-La Roche Ltd: Current Employment. Yaqub: Genentech, Inc./F. Hoffmann-La Roche Ltd: Current Employment. Wei: Genentech, Inc.: Current Employment; F. Hoffmann-La Roche Ltd: Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. O'Hear: Genentech, Inc.: Current Employment; F. Hoffmann-La Roche Ltd: Current holder of individual stocks in a privately-held company. Li: F. Hoffmann-La Roche Ltd: Current Employment. Townsend: F. Hoffmann-La Roche Ltd: Consultancy, Honoraria; Celgene (Bristol-Myers Squibb): Consultancy, Honoraria. OffLabel Disclosure: Mosunetuzumab is a CD20xCD3 bispecific antibody that redirects T cells to engage and eliminate malignant B cells. Mosunetuzumab is an investigational agent.

PURPOSE: This open-label, phase Ib, dose-escalation, and dose-expansion study (NCT01862081) evaluated taselisib with a taxane in locally advanced or metastatic breast cancer (BC) and/or non-small cell lung cancer (NSCLC). METHODS: Patients received taselisib (2-6 mg tablet or 3-6 mg capsule) plus docetaxel or paclitaxel. Primary endpoints were safety, dose-limiting toxicities, maximum tolerated dose, and identification of a recommended phase II dose. Secondary endpoints included pharmacokinetics and antitumor activity assessment. RESULTS: Eighty patients (BC: 72; NSCLC: 7; BC/NSCLC: 1) were enrolled (docetaxel-receiving arms: 21; paclitaxel-receiving arms: 59). Grade ≥ 3 adverse events (AEs), serious AEs, and AEs leading to death were reported in 90.5%, 42.9%, and 14.3% of patients, respectively (docetaxel-receiving arms), and 78.9%, 40.4%, and 3.5% of patients, respectively (paclitaxel-receiving arms). Eight patients experienced dose-limiting toxicities. The maximum tolerated dose was exceeded with 3 mg taselisib (capsule) for 21 consecutive days plus 75 mg/m2 docetaxel and not exceeded with 6 mg taselisib (tablet) for 5 days on/2 days off plus 80 mg/m2 paclitaxel. Objective response rates and clinical benefit rates were 35.0% and 45.0%, respectively (docetaxel-receiving arms), and 20.4% and 27.8%, respectively (paclitaxel-receiving arms). Exposure for paclitaxel or docetaxel plus taselisib was consistent with the single agents. CONCLUSIONS: Taselisib in combination with a taxane has a challenging safety profile. Despite evidence of antitumor activity, the benefit-risk profile was deemed not advantageous. Further development is not planned. ispartof: BREAST CANCER RESEARCH AND TREATMENT vol:178 issue:1 pages:121-133 ispartof: location:Netherlands status: published

Introduction: Mosunetuzumab (M; RG7828) is a full-length, fully humanized immunoglobulin G1 (IgG1) bispecific antibody targeting both CD3 (on the surface of T cells) and CD20 (on the surface of B cells). Clinical data from GO29781 (NCT02500407), a Phase I/Ib study in relapsed or refractory (R/R) non-Hodgkin lymphoma (NHL) pts, indicate that M has promising efficacy and safety (Budde et al. ASH 2018; Bartlett et al. ASCO 2019). We report the characterization of exposure-response (E-R) relationships for safety and efficacy to inform clinical dose/regimen finding. Methods: DATA: Data from Group A (0.05 to 2.8mg q3w dosing) and Group B (0.4/1/2.8 to 1/2/27mg Cycle 1 Day 1/8/15 step-up dosing, followed by q3w dosing) were analyzed. E-R for safety was assessed in 142 evaluable pts by dosing Group. E-R for efficacy was assessed in 130 evaluable pts by aggressive (a) (n=83, primarily DLBCL and transformed FL) and indolent (i) (n=47, primarily FL) NHL histologies. PHARMACOKINETIC (PK) ENDPOINTS: Pt-specific PK exposure metrics, including AUC and Cmax, were derived using a preliminary two-compartment population PK model with time-dependent clearance. Due to the presence of residual rituximab (R) at baseline from prior treatments, an additional exposure metric of average CD20 receptor occupancy (RO%) of M was derived based on the serum PK and binding affinity (KD) of both agents to assess the impact of target binding competition over time. E-R ANALYSES: Objective response rate (ORR), complete response rate (CRR), and adverse event (AE) rates, including cytokine release syndrome (CRS) and neurological AEs (NAE), were summarized by exposure-tertiles and the E-R relationships modeled by logistic regression (linear or Emax models). Response rates and E-R were further assessed in subgroups by RO% tertiles and baseline factors, such as the number of prior lines of therapy, refractory status, lactate dehydrogenase level, and tumor burden, and modeled by multivariate logistic regression. Results: R was present at modest levels at baseline in aNHL pts (median, 3 µg/ml, 33% of pts below quantitation limit [BQL] of 0.5µg/ml) but minimally in iNHL pts (median, Conclusions: E-R analyses indicate promising therapeutic benefit/risk of M in R/R NHL pts. Step-up dosing mitigated CRS-related toxicities, resulting in a broad therapeutic window of M that enables further dose escalation to maximize efficacy. The lack of E-R for safety was contrasted by a steep E-R for efficacy whereby higher M exposures overcome target binding competition in pts with residual R. Our analyses provide useful guidance for the dosing strategy of CD20-targeting T-cell bispecifics. Disclosures Li: F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Bender:Genentech, Inc.: Employment, Equity Ownership. Yin:Genentech, Inc: Employment, Equity Ownership. Li:Pro Unlimited - Genentech, Inc. contractor: Employment; F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Zhang:Genentech, Inc., SSF: Employment. Hernandez:Genentech, Inc.: Employment, Equity Ownership. Kwan:Genentech, Inc: Employment, Equity Ownership. Sun:Harpoon Therapeutics: Employment, Equity Ownership; F. Hoffmann-La Roche Ltd / Genentech, Inc.: Employment. Adamkewicz:Genentech, Inc.: Employment; F. Hoffmann-La Roche Ltd: Equity Ownership. Wang:Genentech, Inc.: Employment; F. Hoffmann-La Roche Ltd: Equity Ownership. Dimier:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Lim:Genentech, Inc.: Employment. O'Hear:F. Hoffmann-La Roche Ltd: Equity Ownership; Genentech, Inc.: Employment. Sehn:Merck: Consultancy, Honoraria; TG Therapeutics: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; TG Therapeutics: Consultancy, Honoraria; Janssen-Ortho: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Astra Zeneca: Consultancy, Honoraria; TEVA Pharmaceuticals Industries: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Morphosys: Consultancy, Honoraria; TEVA Pharmaceuticals Industries: Consultancy, Honoraria; F. Hoffmann-La Roche/Genentech: Consultancy, Honoraria, Research Funding; Apobiologix: Consultancy, Honoraria; Acerta: Consultancy, Honoraria; Kite Pharma: Consultancy, Honoraria; Kite Pharma: Consultancy, Honoraria; Astra Zeneca: Consultancy, Honoraria; Morphosys: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; F. Hoffmann-La Roche/Genentech: Consultancy, Honoraria, Research Funding; Verastem: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Janssen-Ortho: Honoraria; Lundbeck: Consultancy, Honoraria; Acerta: Consultancy, Honoraria; Lundbeck: Consultancy, Honoraria; Merck: Consultancy, Honoraria. Flinn:AbbVie, Seattle Genetics, TG Therapeutics, Verastem: Consultancy; TG Therapeutics, Trillum Therapeutics, Abbvie, ArQule, BeiGene, Curis, FORMA Therapeutics, Forty Seven, Merck, Pfizer, Takeda, Teva, Verastem, Gilead Sciences, Astra Zeneca (AZ), Juno Therapeutics, UnumTherapeutics, MorphoSys, AG: Research Funding; F. Hoffmann-La Roche Ltd: Research Funding; Acerta Pharma, Agios, Calithera Biosciences, Celgene, Constellation Pharmaceuticals, Genentech, Gilead Sciences, Incyte, Infinity Pharmaceuticals, Janssen, Karyopharm Therapeutics, Kite Pharma, Novartis, Pharmacyclics, Portola Pharmaceuticals: Research Funding; TG Therapeutics, Trillum Therapeutics, Abbvie, ArQule, BeiGene, Curis, FORMA Therapeutics, Forty Seven, Merck, Pfizer, Takeda, Teva, Verastem, Gilead Sciences, Astra Zeneca (AZ), Juno Therapeutics, UnumTherapeutics, MorphoSys, AG: Research Funding. Yoon:Novartis: Consultancy, Honoraria; Janssen: Consultancy; Kyowa Hako Kirin: Research Funding; Amgen: Consultancy, Honoraria; Yuhan Pharma: Research Funding; Genentech, Inc.: Research Funding; MSD: Consultancy. Budde:F. Hoffmann-La Roche Ltd: Consultancy. Li:Genentech, Inc. / F. Hoffmann-La Roche Ltd: Employment. Wei:Genentech, Inc./F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. OffLabel Disclosure: Mosunetuzumab (RG7828) is a full-length, fully humanized immunoglobulin G1 (IgG1) bispecific antibody targeting both CD3 (on the surface of T cells) and CD20 (on the surface of B cells). Mosunetuzumab redirects T cells to engage and eliminate malignant B cells. Mosunetuzumab is an investigational agent.

Introduction: Mosunetuzumab (M; RG7828) is a full-length, fully humanized immunoglobulin G1 (IgG1) bispecific antibody targeting both CD3 (on the surface of T cells) and CD20 (on the surface of B cells). It drives tumor B-cell killing independent of T-cell specificity and has been shown clinically to have single-agent activity in relapsed or refractory non-Hodgkin lymphoma, with durable complete responses (CR) at doses as low as 1.2mg (Budde et al. ASH 2018). We present biomarker data from the ongoing first-in-human multicenter Phase I/Ib study GO29781 (NCT02500407), highlighting acute pharmacodynamic effects that confirm mechanism of action (MOA), support Cycle 1 step-up dosing to mitigate cytokine-driven toxicities, and potentially predict response. Methods: Patients (pts) with biomarker data in Group A (0.05 to 2.8mg q3w dosing, n=30) and Group B (0.4/1/2.8 to 1/2/40.5mg Cycle 1 Day 1/8/15 step-up dosing, followed by q3w dosing) were included in the analyses. Peripheral biomarkers were evaluated using whole blood flow cytometry, plasma cytokine ELISA, and ex-vivo single-cell cytokine assay of cryopreserved peripheral blood mononuclear cells. Tumor biomarkers were assessed through CD20 immunohistochemistry and CD8/Ki67 immunofluorescence staining. Average CD20 receptor occupancy (RO%), which takes into account residual levels of rituximab that may compete with M for target binding, was used to characterize the exposure-pharmacodynamic response relationship (Li et al. ASH 2019). Results: Pharmacodynamic changes were observed in peripheral blood by 4 hours (hrs) after infusion of sub-efficacious doses of M in Group A. Transient reduction of circulating T cells was evident starting at the lowest doses administered of 0.05-0.2mg, with decreased cell numbers by 4 hrs after infusion and recovery by 72 hrs. At doses between 0.4-0.8mg, T-cell activation was observed in some pts, as evidenced by upregulation of CD69 on both CD8+ and CD4+ T cells and elevation of IFN-γ in plasma. At 1.2mg (minimal efficacious dose) to 2.8mg, all of these changes were detected in the majority of pts. M induced depletion of circulating B cells immediately after the first dose, which was sustained for the duration of treatment, even in pts refractory to prior anti-CD20 therapy. IL-6 levels peaked within 24 hrs of the Cycle 1 Day 1 dose and the kinetics of IL-6 increase were associated with the onset of cytokine release syndrome (CRS). Hence, step-up dosing at Cycle 1 was implemented in Group B to maintain the IL-6 peak at reasonably low levels and reduce the risk of toxicity. With step-up dosing, pharmacodynamic changes, including transient T-cell decrease, T-cell activation, and cytokine production, remained strongest within 4 hrs of the Cycle 1 Day 1 dose, despite higher subsequent and total cumulative doses. IL-6 peaks were similar in Group A and Group B and were in line with the low grades of CRS observed to date (Schuster et al. ASH 2019). In pts for whom the Cycle 1 Day 1 dose was fixed at 1mg, the acute pharmacodynamic changes were found to be associated with RO% at Day 1. In a subset of diffuse large B-cell lymphoma pts, functional assays showed that peripheral T cells taken at baseline from pts who achieved CR secreted multiple effector cytokines, such as IFN-γ, TNF-α, and Granzyme B, upon M stimulation ex vivo, whereas T cells from pts with progressive disease did not show this capacity. Analysis of tumor biopsies showed similar baseline levels of CD8+ tumor infiltrating T-cells (TILs) between responders and non-responders. M induced increases in CD8+ TILs, which were mostly Ki67-, as early as Cycle 1. The median on-treatment CD8+ TIL level was significantly higher in responders than non-responders. Conclusions: T-cell activation, cytokine elevation, and B-cell depletion in the periphery are among the earliest biomarkers of M activity and precede clinical responses. Acute pharmacodynamic changes confirm the MOA and inform dose/schedule selection. In particular, the 1mg Cycle 1 Day 1 dose, which was chosen to mitigate CRS and to dissociate toxicity and efficacy at higher subsequent doses, still induced potent pharmacodynamic changes. Finally, the data suggest a model whereby clinical efficacy may be critically dependent on activation and migration of functional T cells from the periphery into the tumor bed. Disclosures Hernandez: Genentech, Inc.: Employment, Equity Ownership. Huw:Roche/ Genentech: Employment, Equity Ownership. Belousov:Roche: Employment. Wilson:Genentech, Inc.: Employment. Koeppen:Genentech, Inc.: Employment; Roche: Equity Ownership. McCord:Roche: Equity Ownership; Genentech, Inc.: Employment. Peng:Genentech inc. / Roche: Employment, Equity Ownership. Bartlett:Affimed: Research Funding; Forty Seven: Research Funding; Celgene: Research Funding; Merck: Research Funding; Millennium: Research Funding; Gilead: Research Funding; Genentech, Inc.: Research Funding; Pharmacyclics: Research Funding; Autolus: Research Funding; ADC Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Research Funding; Pfizer: Research Funding; Immune Design: Research Funding; Incyte: Research Funding; Janssen: Research Funding; Kite Pharma: Research Funding; Merck: Research Funding; Millennium: Research Funding; Pfizer: Research Funding; Pharmacyclics: Research Funding; Pharmacyclics: Research Funding; Pfizer: Research Funding; Millennium: Research Funding; Merck: Research Funding; Kite Pharma: Research Funding; Kite Pharma: Research Funding. Budde:F. Hoffmann-La Roche Ltd: Consultancy. Assouline:Pfizer: Consultancy, Honoraria, Speakers Bureau; Abbvie: Consultancy, Honoraria; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Speakers Bureau. Nastoupil:Celgene: Honoraria, Research Funding; Genentech, Inc.: Honoraria, Research Funding; Bayer: Honoraria; Gilead: Honoraria; Janssen: Honoraria, Research Funding; Novartis: Honoraria; TG Therapeutics: Honoraria, Research Funding; Spectrum: Honoraria. Yoon:F. Hoffmann-La Roche Ltd: Research Funding. Matasar:Juno Therapeutics: Consultancy; Merck: Consultancy, Equity Ownership; Roche: Consultancy, Honoraria, Other: Travel, accommodation, expenses , Research Funding; Bayer: Consultancy, Honoraria, Other; Genentech, Inc.: Consultancy, Honoraria, Other: Travel, accommodation, expenses , Research Funding; Seattle Genetics: Consultancy, Honoraria, Other: Travel, accomodation, expenses, Research Funding; Rocket Medical: Consultancy, Research Funding; Teva: Consultancy; Janssen: Honoraria, Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; GlaxoSmithKline: Honoraria, Research Funding; Daiichi Sankyo: Consultancy; Bayer: Other: Travel, accommodation, expenses. Bender:Genentech, Inc.: Employment, Equity Ownership. Kwan:Genentech, Inc: Employment, Equity Ownership. Li:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. O'Hear:F. Hoffmann-La Roche Ltd: Equity Ownership; Genentech, Inc.: Employment. Yin:Genentech, Inc.: Employment, Equity Ownership. Wei:Genentech, Inc./F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Adamkewicz:F. Hoffmann-La Roche Ltd: Equity Ownership; Genentech, Inc.: Employment. OffLabel Disclosure: Mosunetuzumab (RG7828) is a full-length, fully humanized immunoglobulin G1 (IgG1) bispecific antibody targeting both CD3 (on the surface of T cells) and CD20 (on the surface of B cells). Mosunetuzumab redirects T cells to engage and eliminate malignant B cells. Mosunetuzumab is an investigational agent.

7518 Background: T-cell directed therapies (e.g., CAR-T, blinatumomab) are associated with significant risk of Grade (Gr) ≥3 neurotoxicity and CRS/infusion-related reaction (IRR). Mosunetuzumab is a CD20/CD3 bispecific antibody that directs T-cells to engage and eliminate malignant B-cells. We report safety results from an ongoing phase 1/1b study of mosunetuzumab in patients (pts) with R/R B-cell NHL. Methods: Pts received ascending doses on Day 1, Day 8, and Day 15 of Cycle 1 (step-fractionation), then a fixed dose on Day 1 of every 21-day cycle thereafter, up to a maximum of 17 cycles. Primary outcome measures included safety and efficacy. Results: As of October 23, 2018, 114 pts who received step-fractionated dosing of mosunetuzumab were evaluable for safety (Table). The majority of adverse events (AE) occurred during Cycle 1 and 2. Neurologic AEs (NAE), defined from Nervous System or Psychiatric System Organ Classes, were mostly low grade, transient (median duration 4 days) and reversible; most common ones were headache (14%) and dizziness (8%). Gr ≥3 NAEs occurred in 4 pts (4%) with only 1 treatment-related event (hepatic encephalopathy). CRS/IRR was reported in 25% of pts, with only 1 Gr 3 event. Most common CRS symptoms were pyrexia (86%), chills (38%), and tachycardia and headache (14% each). There were no Gr 5 events related to CRS or NAEs. No apparent dose toxicity relationship was observed with step-fractionation in these pts, despite escalation of the Cycle 1 Day 15 dose to 20 mg, consistent with observed peak IL-6 levels after a low Cycle 1 Day 1 dose. In these pts, objective responses were observed in 24/73 (33%; complete response [CR], 13 [18%]) aggressive NHL and 17/32 (53%; CR, 10 [31%]) indolent NHL pts. Conclusions: Step-fractionation has enabled continued dose escalation of mosunetuzumab with no apparent increases in toxicity, exhibiting a promising risk-benefit profile. Clinical trial information: NCT02500407; GO29781. [Table: see text]

There is limited understanding of how signaling pathways are altered by oncogenic fusion transcription factors that drive leukemogenesis. To address this, we interrogated activated signaling pathways in a comparative analysis of mouse and human leukemias expressing the fusion protein E2A-PBX1, which is present in 5%–7% of pediatric and 50% of pre-B-cell receptor (preBCR+) acute lymphocytic leukemia (ALL). In this study, we describe remodeling of signaling networks by E2A-PBX1 in pre-B-ALL, which results in hyperactivation of the key oncogenic effector enzyme PLCγ2. Depletion of PLCγ2 reduced proliferation of mouse and human ALLs, including E2A-PBX1 leukemias, and increased disease-free survival after secondary transplantation. Mechanistically, E2A-PBX1 bound promoter regulatory regions and activated the transcription of its key target genes ZAP70, SYK, and LCK, which encode kinases upstream of PLCγ2. Depletion of the respective upstream kinases decreased cell proliferation and phosphorylated levels of PLCγ2 (pPLCγ2). Pairwise silencing of ZAP70, SYK, or LCK showed additive effects on cell growth inhibition, providing a rationale for combination therapy with inhibitors of these kinases. Accordingly, inhibitors such as the SRC family kinase (SFK) inhibitor dasatinib reduced pPLCγ2 and inhibited proliferation of human and mouse preBCR+/E2A-PBX1+ leukemias in vitro and in vivo. Furthermore, combining small-molecule inhibition of SYK, LCK, and SFK showed synergistic interactions and preclinical efficacy in the same setting. Our results show how the oncogenic fusion protein E2A-PBX1 perturbs signaling pathways upstream of PLCγ2 and renders leukemias amenable to targeted therapeutic inhibition. Cancer Res; 76(23); 6937–49. ©2016 AACR.

Background: PIK3CA, a gene that encodes the α-isoform of the catalytic subunit of Class I PI3K (PI3Kα), is frequently mutated or amplified in solid tumors. Taselisib is an oral, potent, selective inhibitor of Class I PI3Kα, γ, and δ isoforms with enhanced activity against PIK3CA-mutated cancer models. Preclinical and clinical data demonstrated that single-agent taselisib has activity in multiple PIK3CA-mutated tumor types. Methods: This open-label phase I study (Cohort X of PMT4979g; NCT01296555) enrolled patients (pts) with PIK3CA-mutated tumors who had progressed after, or failed to respond to, at least one prior treatment regimen and were not candidates for regimens known to provide clinical benefit. Pts received single-agent taselisib (4 or 6 mg tablet, daily). Eleven subcohorts comprised various solid tumor types: endometrial, bladder, head and neck squamous cell carcinoma (HNSCC), cervical, gastric/gastroesophageal junction, small cell lung, triple-negative breast, colorectal (excluding KRAS-mutated tumors), squamous (excluding histologies in the other subcohorts), ovarian, and pts with PIK3CA mutant tumors not otherwise specified (excluding breast, colorectal, and non-small-cell lung cancers). Tumor tissue (archival or fresh) was assessed centrally for PIK3CA mutation or amplification. The primary endpoint was tolerability and safety of taselisib. Other endpoints included assessment of antitumor activity per Response Evaluation Criteria In Solid Tumors (RECIST) v1.1. Results: At data cutoff (May 1, 2017), 146 pts have been enrolled. Overall, the most common adverse events (AEs; ≥30% of pts) were diarrhea (58.2%), nausea (39.0%), hyperglycemia (31.5%), and fatigue (30.8%). Ninety-four pts (64.4%) experienced ≥1 grade ≥3 AE and 53 pts (36.3%) had grade ≥3 AEs related to taselisib. Sixty-eight pts (46.6%) had serious AEs (SAEs) and the most common SAEs (>2 pts) related to taselisib treatment were colitis (5.5%), diarrhea (4.1%), and hyperglycemia (3.4%). Nine pts (6.2%) had grade 5 events; one AE with a fatal outcome (0.7%) was assessed by the investigator as related to taselisib (septic shock). AEs that led to dose reduction, interruption, or withdrawal were reported in 34 pts (23.3%), 59 pts (40.4%), and 14 pts (9.6%), respectively. Overall, confirmed response rates were 8.9% (n=13) and clinical benefit rates (confirmed response or without disease progression for ≥6 months) were 12.3% (n=18). Confirmed responses were observed in pts with endometrial cancer (2/10 [20.0%]), HNSCC (4/21 [19.0%]), and cervical cancer (2/19 [10.5%]), as well as other tumor types. Conclusions: Single-agent taselisib had an acceptable safety profile (with AEs that were generally reversible and manageable; no new safety signals were identified) and preliminary clinical activity in pts with PIK3CA-mutated locally advanced or metastatic solid tumors. Citation Format: Komal Jhaveri, Dejan Juric, Cristina Saura, Andrés Cervantes, Anton Melnyk, Manish R. Patel, Mafalda Oliveira, Valentina Gambardella, Vincent Ribrag, Cynthia X. Ma, Raid Aljumaily, Philippe L. Bedard, Jasgit C. Sachdev, John Bond, Surai Jones, Timothy R. Wilson, Michael C. Wei, José Baselga. A phase I basket study of the PI3K inhibitor taselisib (GDC-0032) in PIK3CA-mutated locally advanced or metastatic solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT046.

The genetic programs that maintain leukemia stem cell (LSC) self-renewal and oncogenic potential have been well defined, however the comprehensive epigenetic landscape that sustains LSC cellular identity and functionality is less well established. We report that LSCs in MLL-associated leukemia reside in an epigenetic state of relative genome-wide high-level H3K4me3 and low level H3K79me2. LSC differentiation is associated with reversal of these broad epigenetic profiles, with concomitant down-regulation of crucial MLL target genes and the LSC maintenance transcriptional program that is driven by loss of H3K4me3 but not H3K79me2. The H3K4-specific demethylase KDM5B negatively regulates leukemogenesis in murine and human MLL-rearranged AML cells, demonstrating a crucial role for the H3K4 global methylome in determining leukemia stem cell fate.

TPS11621Background: The phosphoinositide 3-dependent kinase (PI3K) pathway is important for cancer growth, proliferation, and survival. PI3K is frequently activated in solid tumors due to amplifica...

520Background: The PI3K pathway is activated in HR+ BC, often via gain-of-function mutations in PIK3CA that occur in ~40% of HR+ BC. Taselisib is a potent and selective PI3K inhibitor, with greater selectivity against mutant PI3Kα isoforms than wild type (WT) PI3Kα. Phase Ib data demonstrated good tolerability and preliminary efficacy for taselisib + F in HR+ BC. Methods: This Phase II, open-label, single-arm study enrolled post-menopausal pts with HER2-, HR+ locally advanced or metastatic BC (mBC) who had progression or non-response to ≥ 1 prior endocrine therapy in adjuvant or mBC settings. Pts received taselisib (6 mg capsule PO qd) plus F (500 mg IM on Cycle 1 Day 1, Cycle 1 Day 15, then q4w Day 1 of each cycle) until progressive disease or unacceptable toxicity. PIK3CA mutation status was centrally confirmed retrospectively on archival tumor tissue by 'cobas' PIK3CA Mutation Test. Primary endpoints were objective response rate (RECIST version 1.1) and clinical benefit rate (CBR; confirmed CR and PR, ...

Disseminated infection due to nontuberculous Mycobacterium (NTM) species is rare in pediatrics. Here we report 6 infections affecting 5 patients at a single institution in an immunocompromised population of pediatric oncology and stem cell transplant recipients. The patients presented within a 1-year period with catheter-associated bacteremia. New pulmonary nodules were noted in 4 of the 5 patients. All of the infections were due to rapidly growing NTM. Patients were successfully treated with removal of the infected catheter and combination antibiotic therapy. There are currently no consensus guidelines for treatment of NTM infections in this population, and a therapeutic approach is presented here.