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PURPOSE Magrolimab is a monoclonal antibody that blocks cluster of differentiation 47, a don't-eat-me signal overexpressed on cancer cells. Cluster of differentiation 47 blockade by magrolimab promotes macrophage-mediated phagocytosis of tumor cells and is synergistic with azacitidine, which increases expression of eat-me signals. We report final phase Ib data in patients with untreated higher-risk myelodysplastic syndromes (MDS) treated with magrolimab and azacitidine (ClinicalTrials.gov identifier: NCT03248479 ). PATIENTS AND METHODS Patients with previously untreated Revised International Prognostic Scoring System intermediate-/high-/very high-risk MDS received magrolimab intravenously as a priming dose (1 mg/kg) followed by ramp-up to a 30 mg/kg once‐weekly or once‐every-2-week maintenance dose. Azacitidine 75 mg/m2 was administered intravenously/subcutaneously once daily on days 1-7 of each 28-day cycle. Primary end points were safety/tolerability and complete remission (CR) rate. RESULTS Ninety-five patients were treated. Revised International Prognostic Scoring System risk was intermediate/high/very high in 27%, 52%, and 21%, respectively. Fifty-nine (62%) had poor-risk cytogenetics and 25 (26%) had TP53 mutation. The most common treatment-emergent adverse effects included constipation (68%), thrombocytopenia (55%), and anemia (52%). Median hemoglobin change from baseline to first postdose assessment was −0.7 g/dL (range, −3.1 to +2.4). CR rate and overall response rate were 33% and 75%, respectively. Median time to response, duration of CR, duration of overall response, and progression-free survival were 1.9, 11.1, 9.8, and 11.6 months, respectively. Median overall survival (OS) was not reached with 17.1-month follow-up. In TP53-mutant patients, 40% achieved CR with median OS of 16.3 months. Thirty-four patients (36%) had allogeneic stem-cell transplant with 77% 2-year OS. CONCLUSION Magrolimab + azacitidine was well tolerated with promising efficacy in patients with untreated higher-risk MDS, including those with TP53 mutations. A phase III trial of magrolimab/placebo + azacitidine is ongoing (ClinicalTrials.gov identifier: NCT04313881 [ENHANCE]).

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Purpose:Atezolizumab [anti–programmed death-ligand 1 (PD-L1)] selectively targets PD-L1 to block its interaction with receptors programmed death 1 and B7.1, thereby reinvigorating antitumor T-cell activity. We evaluated the long-term safety and activity of atezolizumab, along with biological correlates of clinical activity endpoints, in a cohort of patients with melanoma in an ongoing phase Ia study (NCT01375842).Patients and Methods:Patients with unresectable or metastatic melanoma were enrolled to receive atezolizumab 0.1 to 20 mg/kg or ≥10 mg/kg every 3 weeks. Primary study objectives were safety and tolerability. Secondary objectives included investigator-assessed efficacy measures; pharmacodynamic and predictive biomarkers of antitumor activity were explored.Results:Forty-five patients were enrolled and were evaluable for safety. Most treatment-related adverse events (AE) were grade 1/2 (60%). Fatigue (44%), pruritus (20%), pyrexia (18%), and rash (18%) were the most common treatment-related AEs of any grade. No treatment-related deaths occurred. Overall response rate was 30% among 43 efficacy- evaluable patients, with a median duration of response of 62 months [95% CI, 35–not estimable (NE)]. Clinically meaningful long-term survival was observed, with a median overall survival of 23 months (95% CI, 9–66). Baseline biomarkers of tumor immunity [PD-L1 expression on immune cells, T effector (Teff), and antigen presentation gene signatures) and tumor mutational burden (TMB) were associated with improved response, progression-free survival, and overall survival.Conclusions:Atezolizumab was well tolerated, with durable responses and survival in patients with melanoma. PD-L1 expression, TMB, and Teff signatures may indicate improved benefit with atezolizumab in these patients.

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Purpose:Atezolizumab [anti–programmed death-ligand 1 (anti-PD-L1)] is well tolerated and efficacious in multiple cancers, but has not been previously evaluated in metastatic castration-resistant prostate cancer (mCRPC). This study examined the safety, efficacy, and biomarkers of atezolizumab monotherapy for mCRPC.Patients and Methods:This phase Ia, open-label, dose-escalation and dose-expansion study (PCD4989g) enrolled patients with mCRPC who had progressed on sipuleucel-T or enzalutamide. Atezolizumab was given intravenously every 3 weeks until confirmed disease progression or loss of clinical benefit. Prespecified endpoints included safety, efficacy, biomarker analyses, and radiographic assessments.Results:All 35 evaluable patients [median age, 68 years (range, 45–83 years)] received atezolizumab after ≥1 prior line of therapy; 62.9% of patients had received ≥3 prior lines. Treatment-related adverse events occurred in 21 patients (60.0%), with no deaths. One patient had a confirmed partial response (PR) per RECIST 1.1, and 1 patient had a PR per immune-related response criteria. The confirmed 50% PSA response rate was 8.6% (3 patients). Median overall survival (OS) was 14.7 months [95% confidence interval (CI): 5.9–not evaluable], with a 1-year OS rate of 52.3% (95% CI: 34–70); 2-year OS was 35.9% (95% CI: 13–59). Median follow-up was 13.0 months (range, 1.2–28.1 months). Biomarker analyses showed that atezolizumab activated immune responses; however, a composite biomarker failed to reveal consistent correlations with efficacy.Conclusions:Atezolizumab was generally well tolerated in patients with mCRPC, with a safety profile consistent with other tumor types. In heavily pretreated patients, atezolizumab monotherapy demonstrated evidence of disease control; however, its limited efficacy suggests a combination approach may be needed.

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: Atezolizumab [anti–programmed death-ligand 1 (anti-PD-L1)] is well tolerated and efficacious in multiple cancers, but has not been previously evaluated in metastatic castration-resistant prostate cancer (mCRPC). This study examined the safety, efficacy, and biomarkers of atezolizumab monotherapy for mCRPC. Patients and Methods: This phase Ia, open-label, dose-escalation and dose-expansion study (PCD4989g) enrolled patients with mCRPC who had progressed on sipuleucel-T or enzalutamide. Atezolizumab was given intravenously every 3 weeks until confirmed disease progression or loss of clinical benefit. Prespecified endpoints included safety, efficacy, biomarker analyses, and radiographic assessments. Results: All 35 evaluable patients [median age, 68 years (range, 45–83 years)] received atezolizumab after ≥1 prior line of therapy; 62.9% of patients had received ≥3 prior lines. Treatment-related adverse events occurred in 21 patients (60.0%), with no deaths. One patient had a confirmed partial response (PR) per RECIST 1.1, and 1 patient had a PR per immune-related response criteria. The confirmed 50% PSA response rate was 8.6% (3 patients). Median overall survival (OS) was 14.7 months [95% confidence interval (CI): 5.9–not evaluable], with a 1-year OS rate of 52.3% (95% CI: 34–70); 2-year OS was 35.9% (95% CI: 13–59). Median follow-up was 13.0 months (range, 1.2–28.1 months). Biomarker analyses showed that atezolizumab activated immune responses; however, a composite biomarker failed to reveal consistent correlations with efficacy. Conclusions: Atezolizumab was generally well tolerated in patients with mCRPC, with a safety profile consistent with other tumor types. In heavily pretreated patients, atezolizumab monotherapy demonstrated evidence of disease control; however, its limited efficacy suggests a combination approach may be needed.

Introduction: Diffuse large B-cell lymphoma (DLBCL) is a significant source of cancer morbidity and mortality. More than half of all newly diagnosed patients are older than 65 years, among whom the 5-year relative survival rate is 54% (SEER 2020). Prior research has shown that not all elderly patients (≥80 years old) receive R-CHOP or mini-R-CHOP regimens as the first line of therapy (LoT); those who do not may have suboptimal outcomes (Williams, et al. Cancer 2015; Hamlin, et al. Oncologist 2014; Juul, et al. Eur J Cancer 2018). This study leverages two real-world data (RWD) sources, Flatiron Health (FH) electronic health record-derived de-identified database and SEER-Medicare (SEER-M) to characterize elderly patients with DLBCL (including observed treatment patterns), summarize overall survival (OS) outcomes, and identify unmet medical needs in this population. Methods: RWD from FH included patients with a DLBCL diagnosis on or after January 1, 2011, with follow-up until May 31, 2020. The SEER-M database is a linkage of two population-based RWD sources: the SEER Cancer Registry and Medicare claims database. RWD from SEER-M for this study included patients with a DLBCL diagnosis between January 1, 2011 and December 31, 2015, with follow-up until December 31, 2016. All fee-for-service Medicare enrollees in SEER-M had to have complete claims. RWD for basic demographics, treatments and outcomes were analyzed from both datasets; FH's database included data on certain clinical characteristics including granularity for dosing data when available, in comparison to SEER-M. This descriptive analysis included patients who were aged ≥80 years at diagnosis. Among patients in the FH database who received R-CHOP as first LoT and had available dosing data, those who received Results: The study included 725 patients from the FH database and 2613 patients from the SEER-M database; patient characteristics and outcomes were generally consistent between the two datasets. In total, 16% and 35% of the elderly patients had no record of systemic treatment in FH and SEER-M respectively (Table). More than half of the treated patients received R-CHOP in the first LoT (63% and 53% in FH and SEER-M, respectively); other patients received attenuated regimens, including rituximab plus bendamustine (R-Benda), rituximab plus cyclophosphamide, vincristine and prednisolone (R-CVP), and rituximab (R) monotherapy. Patients who received R-CHOP in the first LoT had numerically longer median OS (Flatiron: 55.0 months [95% CI: 41.8-NA]; SEER-M: 50.7 months [95% CI: 45.9-62.9]) compared with those who received other regimens (Figure A, B). Untreated patients had a median survival of 3.1 months (95% CI: 2.3-5.2) in the Flatiron dataset and 2.0 months (95% CI: 1.8-2.2) in the SEER-M dataset. Among those who received R-CHOP and with available dosing data, 51% received reduced-dose R-CHOP in the first LoT and OS appeared shorter than for patients who received full-dose R-CHOP (Figure C). Conclusions: Despite differences between the databases, RWD in FH and SEER-M both demonstrate considerable variation in the regimens received by elderly DLBCL patients, with 16-35% receiving no treatment and >50% receiving attenuated regimens including reduced-dose R-CHOP. Patients receiving regimens other than R-CHOP had a numerically lower survival probability compared with the standard of care (SoC) R-CHOP/reduced-dose R-CHOP. These data show a high unmet medical need among elderly patients with DLBCL who may not be able to tolerate immunochemotherapy regimens that have been evaluated in trials for a carefully selected patient population. Further research will aim to assess prognostic factors at the time of treatment initiation, as well as gather information on comorbidities and other factors that may prevent elderly patients from receiving SoC R-CHOP; these patients may be candidates for better-tolerated novel approaches. Disclosures Shewade: Genentech, Inc.: Current Employment. Olszewski:TG Therapeutics: Research Funding; Adaptive Biotechnologies: Research Funding; Genentech, Inc.: Research Funding; Spectrum Pharmaceuticals: Research Funding. Pace:Genentech, Inc.: Current Employment; Exponent: Ended employment in the past 24 months; Prior employer was a consulting firm. No expert testimony given. No relevant consulting work done.: Consultancy. Surinach:Seattle Genetics: Research Funding. Sellam:F. Hoffmann-La Roche: Current Employment. Mueller:Genentech, Inc.: Current Employment, Ended employment in the past 24 months; F. Hoffmann-La Roche: Current equity holder in publicly-traded company. O'Hear:Genentech, Inc.: Current Employment; F. Hoffmann-La Roche: Current equity holder in publicly-traded company.

Introduction: Up to 30% of patients (pts) aged ≥75 years do not receive standard chemoimmunotherapy (CIT) as first-line (1L) treatment for diffuse large B-cell lymphoma (DLBCL) due to concerns about frailty and comorbidities. Poor outcomes are commonly reported for elderly/unfit pts with 1L DLBCL who receive no treatment, reduced-dose R-CHOP or other therapies such as R-CVP and R-bendamustine (Morrison, et al. J Geriatr Oncol 2020); less toxic, efficacious alternatives to full-dose CIT are needed. Mosunetuzumab (Mosun) is a full-length, fully humanized IgG1 CD20/CD3 bispecific antibody that redirects T cells to engage and eliminate malignant B cells. Single-agent Mosun has shown promising efficacy (including durable complete responses [CRs]) and tolerable safety in relapsed/refractory DLBCL pts in an ongoing Phase I study (GO29781; NCT02500407; Bartlett, et al. ASCO 2019, Schuster, et al. ASH 2019). Here we present early clinical data with Mosun as 1L therapy for elderly/unfit pts with DLBCL. Methods: GO40554 (NCT03677154) is a Phase I/II, open-label, multicenter study. We report data from Cohort B, designed to evaluate the safety, pharmacokinetics (PK) and preliminary efficacy of Mosun in pts with 1L DLBCL who are unable to tolerate full-dose CIT. Two safety evaluation cohorts were planned to receive Mosun at 13.5mg and 30mg, followed by an expansion phase. No safety concerns emerged following evaluation of the two safety cohorts. Eligible pts were aged ≥80 years or 60-79 years with impairment in ≥1 activity of daily living (ADL) or instrumental ADL, or with impairment in cardiac, renal or liver function precluding the use of full-dose CIT. After optional pre-phase treatment with prednisone with or without vincristine, pts received Mosun intravenously with step-up dosing on Day (D) 1, 8 and 15 of Cycle (C) 1, followed by a fixed dose on D1 of each subsequent 21-day cycle. Interim response assessment (IRA) occurred after C4 and primary response assessment (PRA) occurred after C8, with an option to continue up to maximum 17 cycles in case of partial remission (PR) following PRA. Results: As of May 27, 2020, 19 pts in Cohort B had received Mosun (1mg [C1 D1]/2mg [C1 D8]/13.5mg [C1 D15 onwards], n=8; 1/2/30mg, n=11). Eight pts were enrolled in the 13.5mg safety evaluation cohort and 11 enrolled in the 30mg safety cohort and expansion (7+4 respectively). Median age was 84 (range: 67-100) years, 14 (74%) pts were women, 10 (53%) had Ann Arbor stage III-IV and 17 (90%) had an IPI score ≥2. Median Mosun cycles received was 6 (range: 2-9; one pt in PR continued treatment). Among 19 pts, 16 (84%) had ≥1 adverse event (AE), 13 (68%) had ≥1 AE related to Mosun and 7 (37%) experienced a Grade (Gr) 3-4 AE, of which 4 were related to Mosun. No fatal AEs were observed. The most common (>10%) treatment-emergent AEs were cytokine release syndrome (CRS; n=9, 47%), rash (n=4, 21%), neutropenia, nausea, decreased appetite, dry mouth, fatigue, pain and muscle spasms (all n=2, 11%). All CRS events were Gr 1 by ASTCT consensus criteria (Lee, et al. Biol Blood Marrow Transplant 2019); no pts experienced hypotension, hypoxia or required tocilizumab or steroid treatment. No severe (Gr ≥3) neurologic AEs were observed. Gr 2 (ICAN) neurotoxicity was observed in one (5%) pt on C1D2 with symptoms of inability to answer questions, drowsiness, weakness and somnolence, combined with Gr 1 CRS (fever and tachycardia). The event resolved after 2 days and was considered related to Mosun. Eight (42%) pts discontinued Mosun early due to progressive disease (PD) between C2-C6. No pts discontinued Mosun due to an AE. Among all treated pts, the overall response rate was 58% (11/19) and CR rate was 42% (8/19). At Mosun dose 13.5mg, 3/8 pts (38%) achieved a CR, 2 (25%) had a PR and 3 (38%) had PD at the PRA. At Mosun dose 30mg, response was available at IRA: 5/11 pts (45.5%) achieved a CR, 1 (9%) had a PR and 5 (45.5%) had PD. Of the 8 pts with PD (from both dosing cohorts), 5 have received salvage therapy post progression. Figure 1 shows a durable response of almost a year for the first responder. Correlative studies of T-cell response by flow cytometry and cytokine expression, and PK analyses are ongoing and will be provided. Conclusions: Early clinical data indicate that single-agent Mosun confers notable efficacy and remarkable tolerability for previously untreated elderly/unfit DLBCL pts. Mosun is a promising chemotherapy-free regimen for patients who otherwise have limited options. Disclosures Olszewski: Spectrum Pharmaceuticals: Research Funding; TG Therapeutics: Research Funding; Adaptive Biotechnologies: Research Funding; Genentech, Inc.: Research Funding. Avigdor:Takeda, Gilead, Pfizer: Consultancy, Honoraria; Janssen, BMS: Research Funding. Babu:Amgen: Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding; Fort Wayne Medical Oncology & Hematology: Current Employment, Current equity holder in publicly-traded company; Lilly: Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding; Sanofi: Research Funding; Janssen Oncology: Research Funding; Lutheran Hospital: Other; Bayer: Honoraria; AstraZeneca: Consultancy, Honoraria; AstraZeneca/MedImmune: Research Funding; Boehringer Ingelheim: Consultancy; Alexion Pharmaceuticals: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company), Research Funding, Speakers Bureau; Argenx: Consultancy, Research Funding; Novartis: Research Funding; Genentech, Inc./ F. Hoffmann-La Roche: Research Funding; Syndax: Research Funding; Nektar: Research Funding; Merck: Research Funding; AbbVie: Research Funding; TG Therapeutics: Research Funding. Levi:Abbvie Inc: Consultancy, Research Funding. Abadi:Abbvie Inc: Research Funding; Roche, Gilead, Abbvie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Holmes:Texas Oncology PA: Current Employment; Gilead/Kite, Celgene/Juno, Rigel, Karyopharm, Janssen, Dova: Consultancy; Gilead/Kite, Novartis, Autolus, Celgene/Juno/bluebird, Genentech, Inc., Rigel, Janssen, Unum, ADC Therapeutics, Seattle Genetics, Incyte, Verastem: Research Funding; Kite, Karyopharm, Seattle Genetics, Rigel, Dova: Speakers Bureau. McKinney:UNUM, Molecular Templates, Incyte, Beigene, Denovo Biopharma, Pharmacyclics, Nordic Nanovector, BMS, Genentech, Inc., Celgene: Research Funding; Kite/Gilead: Honoraria, Speakers Bureau; Kite/Gilead, Seattle Genetics, Molecular Templates, BTG, Pharmacyclics, Verastem, Genentech, Inc., Celgene: Consultancy. McCord:F. Hoffmann-La Roche: Current equity holder in publicly-traded company; Genentech, Inc.: Current Employment. Xie:F. Hoffmann-La Roche: Current Employment. Chen:Janssen Pharmaceuticals: Current equity holder in publicly-traded company; Bristol-Myer Squibb: Current equity holder in publicly-traded company, Ended employment in the past 24 months; Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company. Sarouei:Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company. Qayum:F. Hoffmann-La Roche: Current Employment. O'Hear:Genentech, Inc.: Current Employment; F. Hoffmann-La Roche: Current equity holder in publicly-traded company. Sellam:F. Hoffmann-La Roche: Current Employment. Eradat:UCLA Medical Center, David Geffen school of Medicine at UCLA: Current Employment; Genentech, Inc.: Consultancy, Honoraria, Research Funding, Speakers Bureau; F. Hoffmann-La Roche: Consultancy, Research Funding; Abbvie: Consultancy, Honoraria, Research Funding, Speakers Bureau; Astrazeneca, Atara, Kite, Juno, Acerta, BeiGene, Celgene: Research Funding. OffLabel Disclosure: Mosunetuzumab (RG7828; CD20-TDB) 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.

Context Mosun, a full-length, humanized, IgG1 CD20×CD3 bispecific antibody, demonstrated efficacy/safety in relapsed/refractory DLBCL (NCT02500407; Schuster, et al. ASH 2019). The phase I/II multicenter GO40554 (NCT03677154) study showed similar results for elderly/unfit patients with first-line DLBCL intolerant of full-dose chemoimmunotherapy (CIT) (Olszewski, et al. ASH 2020). Objective To describe updated GO40554 study data. Methods Two safety-evaluation cohorts were assessed (Mosun 13.5 mg and 30 mg), then a 30 mg expansion phase. Patients were aged ≥80 years; 60–79 years with impairment in ≥1 activity of daily living (ADL); instrumental ADL; or impaired cardiac, renal, or liver function. Patients received optional pre-treatment with prednisone (+/– vincristine), then intravenous mosun in step-up doses on days (D)1 (1 mg), 8 (2 mg), and 15 (full-dose: 13.5/30 mg) of cycle (C)1, and full (C1D15) dose on D1 of each 21-day cycle for eight cycles, continuing for ≤17 cycles. Results As of January 15, 2021, 40 patients received mosun (13.5 mg safety cohort, n=8; 30 mg safety cohort, n=7; 30 mg expansion, n=25). Median age: 84 (range 67–100) years; 50% with Ann Arbor Stage III–IV, 80% with IPI score ≥2. Of 40 treated patients, 27 (67.5%) had ≥1 mosun-related adverse event (AE); 15 (37.5%) had a grade 3–4 AE. Most common treatment-emergent AE: cytokine release syndrome (CRS; n=9, 22.5%); five patients had neutropenia (12.5%). Six (15%) patients had grade 1 CRS per ASTCT (Lee, et al. Biol Blood Marrow Transplant 2019); three (7.5%) had grade 2 CRS, all managed with supportive care, fluids for hypotension, steroids, or low-flow oxygen, as required (no tocilizumab, vasopressors, high-flow oxygen, or intensive care). 14 (35%) patients discontinued due to progressive disease (PD). Overall response rate for efficacy-evaluable patients (n=31): 67.7%; complete response (CR) rate: 41.9%. Responses with 13.5 mg mosun: CR: 37.5%; PR: 37.5%; PD: 25%; with 30 mg mosun: CR: 43.5%; PR: 21.7%; stable disease/PD: 34.8%. Four durable responses were observed ≥12 months from start of therapy in 13 patients with CR (11 ongoing). Conclusions Mosun showed promising efficacy, including durable responses, and tolerable safety for elderly/unfit patients with 1L DLBCL; it should be further evaluated as a chemotherapy-free backbone for patients unable to tolerate standard CIT.

Context Mosunetuzumab (Mosun), a full-length, humanized, IgG1 CD20xCD3 bispecific antibody, showed promising efficacy/safety for R/R B-NHL (NCT02500407; Assouline, et al. ASH 2020). Mosun combined with the anti-CD79b antibody-drug conjugate Pola showed synergistic anti-lymphoma activity in a mouse xenograft model, supporting the Phase Ib/II, open-label, multicenter trial of Mosun-Pola for R/R B-NHL (GO40516, NCT03671018). Objective To present early clinical data from the Phase Ib cohort of GO40516. Methods Patients with R/R follicular lymphoma (FL, grade 1–3a) or aggressive NHL (aNHL), including de novo diffuse large B-cell lymphoma (DLBCL), transformed FL (trFL), and grade 3b FL (FL3b), received Cycle (C)1 step-up doses of Mosun on Day (D)1 (1 mg) and D8 (2 mg), and target dose on C1D15, continuing from C2D1. Mosun was given every 21 days for eight cycles, continuing for ≤17 cycles. Pola (1.8 mg/kg) was administered with Mosun on D1 of six cycles. Results As of November 17, 2020, 22 patients received Mosun-Pola (Mosun target doses: 9 mg, n=7; 20 mg, n=3; 40 mg, n=6; 60 mg [D1 dose 30 mg from C3 onward], n=6). Patients had DLBCL (n=12), FL (n=3), FL3b (n=3), and trFL (n=4). Median age: 70 (38–81) years; median 3 (1–10) prior lines of therapy; prior chimeric antigen receptor T-cell (CAR-T) therapy (n=7; 32%). Median follow-up duration: 9.6 (0.7–23.7) months. Most frequent treatment-related adverse events (AEs): neutropenia (45.4%), fatigue, nausea, and diarrhea (all 36.4%). Cytokine release syndrome was observed in two patients (9.1%; both grade 1 [Lee, et al. Biol Blood Marrow Transplant 2019]). One dose-limiting toxicity (grade 3 new-onset atrial fibrillation) was observed in the 40 mg cohort; maximum tolerated dose not exceeded. Most common grade ≥3 AE: neutropenia (n=8; 36.4%). Two (9.3%) grade 5 AEs occurred (sudden cardiac death [n=1]); respiratory failure [n=1]); neither was deemed treatment-related. Complete responses were achieved with Mosun-Pola in patients with R/R aNHL (n=9; 47.4%), prior CAR-T therapy (n=2; 28.6%) and FL (n=3; 100%). Conclusions These data indicate that Mosun-Pola has an acceptable safety profile and shows promising efficacy in patients with predominantly aggressive R/R NHL. The Phase II expansion cohort in patients with R/R DLBCL is ongoing, with no requirement for mandatory hospitalization.

Background: mTNBC represents an area of high unmet need, yet studies assessing real-world outcomes in pts treated in 2L are limited. We describe treatment patterns and outcomes in mTNBC pts receiving 2L treatment primarily in community cancer care clinics in the USA. Methods: Pts aged ≥18 y with a confirmed diagnosis of mTNBC between 1 Jan 2011 and 28 Feb 2017 and who received 2L therapy were identified from the Flatiron Health electronic health record-derived database. Overall survival (OS) and time to next treatment (TTNT) were assessed as primary outcomes using Kaplan–Meier methods in both the overall population and subgroups of pts receiving the most commonly used agents (capecitabine, taxane, gemcitabine). Results: Most of the 623 pts analyzed were White (62.9%) and received care in community clinics (94.9%). The most commonly used previous first-line (1L) regimens in this 2L pt population were: capecitabine (14.0%), cyclophosphamide/doxorubicin (11.6%), carboplatin/gemcitabine (9.3%), paclitaxel (7.1%), and nab-paclitaxel (7.1%); the remaining 51.0% of pts received 95 different 1L regimens. The most common 2L treatments were monotherapy regimens: capecitabine (10.9%), paclitaxel (9.3%), eribulin (9.0%), nab-paclitaxel (8.2%), and gemcitabine (7.7%); the remaining 54.9% of pts received 120 different 2L regimens. Selected demographic, clinical, and treatment characteristics and outcomes after median follow-up of 8.5 (interquartile range [IQR] 4.5–15.7) mo are shown below. No. of pts (%)All pts (n=623)Selected subgroups by agent-containing regimen* Capecitabine (n=101)Taxane (n=222)Gemcitabine (n=111)Median age at initial metastatic diagnosis, y (IQR)58 (50–68)60 (53–67)58 (50–68)61 (51–70)Recurrent458 (73.5)81 (80.2)130 (58.6)93 (83.8)TFI >12 mo†104 (47.1)18 (43.9)21 (42.9)23 (57.5)TFI ≤12 mo†117 (52.9)23 (56.1)28 (57.1)17 (42.5)TFI missing237408153De novo164 (26.3)20 (19.8)92 (41.4)18 (16.2)Missing1 (0.2)000Median time from 1L to start of 2L, mo (IQR)3.7 (2.1–6.4)4.2 (2.6–7.5)2.5 (1.8–4.3)4.1 (2.1–7.1)ECOG PS ≥2 at start of 2L57 (9.1)13 (12.9)15 (6.8)16 (14.4)CNS/brain metastases at start of 2L80 (12.8)14 (13.9)21 (9.5)16 (14.4)Median TTNT‡, mo (95% CI)4.5 (4.1–5.0)4.1 (3.5–5.0)5.5 (4.4–6.2)4.1 (3.1–4.8)Median OS‡, mo (95% CI)10.2 (8.9–11.1)10.0 (8.0–13.5)12.4 (10.6–15.0)8.3 (6.9–9.6)1-y OS‡, % (95% CI)42.3 (38.2–46.4)43.6 (33.3–53.8)51.9 (45.2–58.7)29.3 (20.1–38.6)TFI=treatment-free interval. *Any regimen containing each agent (monotherapy or combination); subgroups not mutually exclusive. †Defined as the interval between last (neo)adjuvant therapy and metastatic diagnosis; percentages calculated using pts with recurrent disease and non-missing TFI as the denominator. ‡From start of 2L Conclusions: There was no clear 2L treatment standard used for mTNBC and median OS was short (10.2 mo overall). Notably, pts receiving 2L gemcitabine- vs taxane-containing therapy experienced shorter median OS and lower 1-y OS rates, although imbalances in prior therapy, disease biology, and demographic and prognostic factors between these subgroups may have contributed to the observed differences. 2L treatment for mTNBC remains an area of high unmet medical need. Citation Format: Luhn P, O'Hear C, Ton TG, Hsieh A, Yi J, Chang C-W, Funke R, Kurian A. Outcomes in patients (pts) with metastatic triple-negative breast cancer (mTNBC) treated in second line (2L) in the US real-world setting [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-14-04.

Background: Cancer immunotherapy (CIT) has significantly improved overall survival across multiple tumor types, but only subsets of patients experience durable response with single-agent CIT. Combinations of CIT with targeted therapy or chemotherapy may be needed in order to target multiple cancer immune escape mechanisms simultaneously, thus providing personalized treatment options that extend clinical benefit to more patients. The MORPHEUS platform includes multiple phase Ib/II trials designed to identify early signals of safety and activity of CIT combinations. Using a randomized trial design, multiple CIT combination arms are compared with a single standard-of-care control arm. These trials have the flexibility to open new treatment arms with novel CIT combinations as they become available and to close arms that show minimal activity or unacceptable toxicity. Here we describe MORPHEUS trials in patients with metastatic or unresectable locally advanced hormone receptor–positive (HR+BC) or triple-negative breast cancer (TNBC), 2 patient populations in need of more treatment options. Trial design: MORPHEUS-HR+BC (NCT03280563) will enroll patients with metastatic or unresectable locally advanced HR+BC who have progressed during or after first-line treatment with a cyclin-dependent kinase (CDK) 4/6 inhibitor and whose tumors do not express human epidermal growth factor 2 (HER2). MORPHEUS-TNBC (NCT03424005) will enroll patients with metastatic or unresectable locally advanced TNBC who have progressed during or after first-line treatment with chemotherapy. For both studies, key inclusion criteria include Eastern Cooperative Oncology Group performance status of 0-1 (stage 1) or 0-2 (stage 2) and measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. Key exclusion criteria include prior treatment with T-cell co-stimulating or immune checkpoint blockade therapies, and symptomatic, untreated, or actively progressing central nervous system metastases. Patients in both trials will be randomized to one of the CIT atezolizumab combination arms or a control arm (up to 5 arms in HR+BC and up to 6 arms in TNBC). Patients experiencing loss of clinical benefit or unacceptable toxicity in stage 1 may be eligible to switch to a different CIT atezolizumab combination arm in stage 2. Primary endpoints are safety measures and investigator-assessed objective response rate per RECIST v1.1. Progression-free survival, overall survival, duration of response, clinical benefit rate (HR+BC) or disease control rate (TNBC) are among the secondary endpoints. Exploratory biomarkers will also be examined. Citation Format: Yardley DA, Abu-Khalaf M, Boni V, Brufsky A, Emens LA, Gutierrez M, Hurvitz S, Im S-A, Loi S, McCune SL, Schmid P, O'Hear C, Zhang X, Vidal GA. MORPHEUS: A phase Ib/II trial platform evaluating the safety and efficacy of multiple cancer immunotherapy combinations in patients with hormone receptor–positive and triple-negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT2-06-04.

Objectives To assess the safety and efficacy of atezolizumab and docetaxel in patients with and without a history of asymptomatic, treated brain metastases in the phase III OAK trial. Materials and methods Patients received 1200 mg atezolizumab or 75 mg/m2 docetaxel every 3 weeks until unacceptable toxicity, disease progression, or loss of clinical atezolizumab benefit. Patients with asymptomatic, treated supratentorial metastases were eligible. Patients had brain scans before enrollment; follow-up brain scans and treatment were required when clinically indicated. Results Approximately 14% of patients in each arm had a history of asymptomatic, treated brain metastases (61/425 in the atezolizumab arm and 62/425 in the docetaxel arm). Fewer treatment-related adverse events (AEs), serious AEs, and treatment-related neurologic AEs were reported with atezolizumab than with docetaxel, regardless of history of asymptomatic, treated brain metastases. In patients with a history of asymptomatic, treated brain metastases, median overall survival (OS) was longer with atezolizumab than with docetaxel (16.0 vs 11.9 months; hazard ratio = 0.74; 95% CI: 0.49–1.13). Median OS was also longer with atezolizumab in patients without a history of asymptomatic, treated brain metastases (13.2 vs 9.3 months; hazard ratio = 0.74; 95% CI: 0.63–0.88). Landmark analyses showed that patients with a history of asymptomatic, treated brain metastases had a lower probability of developing new symptomatic brain lesions with atezolizumab vs docetaxel at 6–24 months. Patients without a history had a lower probability with atezolizumab at 18–24+ months. Conclusion Atezolizumab had an acceptable neurologic safety profile, showed a trend toward an OS benefit, and led to a prolonged time to radiographic identification of new symptomatic brain lesions compared with docetaxel in patients who had a history of asymptomatic, treated brain metastases. Clinicaltrials.gov registration number: NCT02008227.

Introduction Atezolizumab, an anti-programmed death-ligand 1 (PD-L1) antibody, inhibits PD-L1:PD-1 and PD-L1:B7.1 interactions, restoring anticancer immunity. Here, we report final analyses from the non-small-cell lung cancer (NSCLC) cohort of the first atezolizumab phase I study. Methods Patients with NSCLC received atezolizumab 1–20 mg/kg or 1200 mg intravenously every 3 weeks. Baseline PD-L1 expression on tumour cells (TCs) and tumour-infiltrating immune cells (ICs) was assessed (VENTANA SP142 immunohistochemistry assay). Exploratory subgroup analyses investigated responses by baseline PD-L1 expression and oncogenic mutational status. Results Eighty-nine patients, 98% of whom had received previous systemic therapy, were evaluable for safety and antitumour activity. Atezolizumab was well tolerated, with grade III/IV treatment-related adverse events (TRAEs) observed in 10 patients (11%). All-grade TRAEs occurring in >10% of patients were fatigue, nausea and decreased appetite; grade III/IV TRAEs occurring in >2% of patients were fatigue, dyspnoea, hyponatremia and hypoxia. One patient died from treatment-unrelated pneumonia. Objective response rate (ORR) was 50% (95% confidence interval [CI], 28%–72%), 33% (20%–48%), 29% (18%–41%) and 11% (1%–35%) for the TC3 or IC3, TC2/3 or IC2/3, TC1/2/3 or IC1/2/3 and TC0 and IC0 subgroups, respectively. All-patient ORR was 23% (95% CI, 14%–33%). Median duration of response was 16.4 months (range, 7.2–53.4+). One-, 2-, and 3-year survival rates were 63% (95% CI, 53%–73%), 37% (26%–47%) and 28% (18%–38%), respectively. Conclusions Single-agent atezolizumab was well tolerated with long-term clinical benefits, including durable responses and survival, in pretreated NSCLC. Improved responses and survival rates were seen with increasing baseline PD-L1 expression. ClinicalTrials.gov identifier NCT01375842 .

Glioblastoma is the most common primary malignant brain tumor. No standard treatment exists for recurrent disease. Glioblastoma is associated with an immunosuppressive tumor microenvironment. Immune checkpoint inhibitors, including atezolizumab (anti-programmed death-ligand 1), have demonstrated clinical activity in various cancers. Here, we present the safety and efficacy of atezolizumab in patients with glioblastoma from the phase 1a PCD4989g clinical trial (NCT01375842). Eligible patients had confirmed recurrent glioblastoma and measurable disease per RANO criteria. Atezolizumab (1200 mg) was administered intravenously every 3 weeks until progression or unacceptable toxicity. Patients were monitored for safety; response was evaluated at least every 6 weeks. Baseline biomarkers were evaluated. All 16 patients enrolled had received prior chemotherapy, and 50% prior bevacizumab. Ten patients (63%) experienced a treatment-related event. No treatment-related grade 4–5 events were reported. All deaths occurred due to progression or during follow-up. One patient experienced a partial response (5.3 months); 3 experienced disease stabilization. The median overall survival was 4.2 months (range 1.2 to 18.8+ months). Association between peripheral CD4+ T cells and efficacy was observed. Two patients with IDH1-mutant tumors and 1 with a POLE-mutant tumor experienced ≥ 16 months survival. Atezolizumab was safe and well tolerated in this group of patients with recurrent glioblastoma. Our preliminary findings suggest that biomarkers, including peripheral CD4+ T cells and hypermutated tumor status, may help guide selection of patients with recurrent glioblastoma who might receive most benefit from atezolizumab therapy, supporting further atezolizumab combination studies in glioblastoma.

Background: Metastatic triple negative breast cancer (mTNBC) has a poor prognosis with limited treatment options. Atezolizumab (atezo) is a humanized monoclonal antibody that inhibits the binding of PD-L1 to PD-1 and B7.1. Atezo has demonstrated promising activity in the mTNBC cohort of the phase 1 PCD4989g study. Clinical activity was previously linked to higher PD-L1 expression by IHC (ORR: 13% vs 5%) and TILs (ORR: 13% vs 7%) (Schmid et al., AACR 2017, NCT01375842). Here we characterize molecular features of tumors from atezo-treated patients and explore their potential association with clinical activity. Methods & Results: Molecular characterization of pre-treatment tumor tissue was performed to investigate potential biological mechanisms associated with the clinical activity of atezo in mTNBC. DNA mutational analysis of tumors from 78 patients was performed with the Foundation Medicine One panel. Median tumor mutation burden (TMB) was 4.6 Mut/Mb (CI 95% 3.604 - 5.405). TMB was not associated with either TILs or immune biomarkers by IHC (PD-L1 or CD8) or with clinical activity (ORR, PFS or OS). The prevalence of loss of heterozygosity or mutations in TP53 or BRCA1/2 in this mTNBC cohort was 65%, 95%, and 10%, respectively. None of these genomic alterations were associated with clinical activity to atezo. RNA-Seq based analyses were performed in tissue from 96 patients. PAM50 profiling classified these tumors as 84% basal-like, 9% HER-2-enriched, 4% luminal A and 2% luminal B. TNBC subtyping (Burstein et al., CCR 2015) classified 42% of the tumors as basal-like (BL) immune activated (BLIA), 35% BL immune suppressed (BLIS), 17% luminal androgen receptor (LAR) and 2% mesenchymal (MES). Histopathology immune biomarkers TILs, PD-L1 and CD8 were highest in BLIA, intermediate in LAR and lowest in BLIS. ORRs by RECIST 1.1 were highest in BLIA and LAR, and lowest in BLIS and MES (17.5%, 18.8%, 0% and 0%, respectively). Although univariate analysis showed that the BLIA subgroup had significantly longer PFS and OS, multivariate analysis showed an association for both the BLIA and LAR subgroups with improved PFS and OS. High expression of pre-specified B- and T-cell RNA signatures were significantly associated with better ORR, PFS, and OS. Conclusion: Comprehensive molecular characterization of tumors from this non-randomized phase 1 mTNBC cohort showed a low TMB. Mutations in BRCA1/2, TP53, or loss of heterozygosity did not impact atezo clinical activity. Clinical benefit from atezo was enriched in BLIA and LAR TNBC subtypes, both representing tumors with a rich tumor immune microenvironment. Citation Format: Molinero L, Chang C-W, Udyavar A, Fasso M, O'Hear C, Emens L, Cruz C, Hegde P, Schmid P. Molecular characterization of tumors from metastatic TNBC patients treated with atezolizumab (atezo) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-09-13.

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.

Background: Cytokine release syndrome (CRS) is a potentially serious complication of T-cell engaging immunotherapy. Effective measures are needed to reduce the rate and severity. In a multicenter Phase I/II study (NCT02500407), the CD20xCD3 bispecific antibody mosunetuzumab (Mosun) showed durable complete responses (CR) and had manageable safety in patients (pts) with late-line R/R B-NHL (Schuster et al. ASH 2019). IV administration with Cycle (C) 1 step-up dosing was an effective strategy for mitigating CRS during C1 (Bartlett et al. ASCO 2019). Fixed-dose SC administration was also a viable strategy for CRS mitigation, owing to the slower rate of Mosun absorption compared with IV (Matasar et al. ASH 2020). A combination of both strategies could further improve the CRS profile. We present safety and efficacy data from the initial cohorts investigating SC Mosun administration with C1 step-up dosing in the Phase I/II study. Methods: All pts had R/R B-NHL with ≥1 prior line of systemic therapy and ECOG PS ≤1. SC Mosun was given in 21-day cycles using two step-up dosing schedules (C1 day [D]1/C1D8/C1D15 and D1 of subsequent cycles: 5/15/45mg or 5/45/45mg). Mosun was discontinued after C8 in pts who achieved a CR, while pts with a partial response or stable disease continued Mosun for a total of 17 cycles, unless progressive disease or unacceptable toxicity occurred. Primary objectives included evaluation of safety, tolerability, and pharmacokinetics (PK). Responses were evaluated by investigator-assessment of PET/CT scans using Cheson 2007 criteria. CRS is reported using ASTCT criteria (Lee et al. Biol Blood Marrow Transplant 2019). Results: As of June 21, 2021, 74 pts had been enrolled (5/15/45mg: 38 pts; 5/45/45mg: 36 pts). Median age was 67.0 years (range: 41-88). The most common NHL subtypes were DLBCL (31 pts), FL (21), transformed (tr) FL (10), and MCL (3). 70.0% of pts had Ann Arbor stage III or IV disease. Median number of prior lines of therapy was 3 (range: 1-9). 79.5% of pts were refractory to prior anti-CD20 therapy and 82.4% were refractory to their last prior therapy. Median follow-up for safety was 2.5 months (range: 0.2-7.2). No dose-limiting toxicities were observed during dose-escalation. Common all-Grade (Gr) adverse events (AEs; ≥10% of pts) were injection site reaction (52.7%; Gr 1: 47.3%; Gr 2: 5.4%), CRS (24.3%), fatigue (21.6%), headache (17.6%), rash (13.5%), and pyrexia (10.8%). CRS mostly occurred in C1 and was low Gr in all pts (Gr 1: 17.6%; Gr 2: 6.8%); no Gr ≥3 CRS occurred. Gr 2 CRS occurred with a similar frequency in the 5/15/45mg and 5/45/45mg cohorts (7.9% vs 5.6% of pts, respectively). In the 5/15/45mg cohort, the 3 Gr 2 CRS events occurred after each of the C1 doses, while in the 5/45/45mg cohort, the 2 Gr 2 CRS events occurred after the first 45mg dose. Median duration of CRS was 2 days (range: 1-6) and all events resolved without sequelae. Neutropenia occurred in 12.2% of pts (Gr 2: 2.7%; Gr 3: 6.8%; Gr 4: 2.7%). Febrile neutropenia occurred in only 1 pt (Gr 3). Serious infections occurred in 3 pts (2 pneumonia, both resolved; 1 COVID-19, fatal outcome). No Mosun-related Gr 5 (fatal) AEs or Mosun-related AEs leading to Mosun discontinuation occurred. The PK profile of SC Mosun was consistent with that previously reported, with high bioavailability (>85%), a slow absorption rate, and a blunted C max. IL-6 and IFN-y kinetics in plasma were similar in both SC cohorts, with modest and delayed increases observed after the initial dose, contrasting with the more marked and rapid increases observed with IV dosing, and consistent with the low frequency and severity of CRS observed. At data cut-off, 38 pts were efficacy evaluable. Responses were observed in 19 pts across all histologies, including 8/10 (80%) pts with R/R FL and 6/17 (35.3%) pts with R/R DLBCL/trFL. Conclusions: SC Mosun administration with C1 step-up dosing has a favorable safety profile in pts with late-line and highly refractory B-NHL, enabling an outpatient treatment schedule without mandatory hospitalizations. Encouragingly, the 5/45/45mg schedule had a low rate of CRS that was similar to the 5/15/45mg schedule, allowing the target dose to be reached earlier. Early response data suggest that the efficacy of Mosun is not compromised by SC dosing. Compared with IV, SC Mosun is likely to improve convenience for pts and efficiency for healthcare providers. Updated efficacy data with longer follow up and depth of response will be presented. Disclosures Bartlett: Affimed: Research Funding; Autolus: Research Funding; Bristol-Myers Squibb: Research Funding; Celgene: Research Funding; Forty Seven: Research Funding; Janssen: Research Funding; Kite Pharma: Research Funding; Merck: Research Funding; Millennium: Research Funding; Pharmacyclics: Research Funding; Genentech, Inc./F. Hoffmann-La Roche Ltd: Membership on an entity's Board of Directors or advisory committees, Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; ADC Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Washington University School of Medicine: Current Employment. Giri: Royal Adelaide Hospital: Current Employment. Budde: Genentech, Inc.: Consultancy; Merck, Inc: Research Funding; Amgen: Research Funding; AstraZeneca: Research Funding; Mustang Bio: Research Funding; Novartis: Consultancy; Gilead: Consultancy; Roche: Consultancy; Beigene: Consultancy. Schuster: Celgene: Consultancy, Honoraria, Research Funding; Nordic Nanovector: Consultancy; Novartis: Consultancy, Honoraria, Patents & Royalties, Research Funding; Abbvie: Consultancy, Research Funding; Acerta Pharma/AstraZeneca: Consultancy; Alimera Sciences: Consultancy; BeiGene: Consultancy; Juno Theraputics: Consultancy, Research Funding; Loxo Oncology: Consultancy; Tessa Theraputics: Consultancy; Genentech/Roche: Consultancy, Research Funding; Pharmaclyclics: Research Funding; Adaptive Biotechnologies: Research Funding; Merck: Research Funding; Incyte: Research Funding; TG Theraputics: Research Funding; DTRM: Research Funding. Assouline: Johnson&Johnson: Current equity holder in publicly-traded company; Gilead: Speakers Bureau; Amgen: Current equity holder in publicly-traded company, Research Funding; Novartis: Honoraria, Research Funding; Eli Lilly: Research Funding; Roche/Genentech: Research Funding; Jewish General Hospital, Montreal, Quebec: Current Employment; Takeda: Research Funding; BeiGene: Consultancy, Honoraria, Research Funding; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; AstraZeneca: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria. Matasar: Merck Sharp & Dohme: Current holder of individual stocks in a privately-held company; Juno Therapeutics: Consultancy; Janssen: Honoraria, Research Funding; Daiichi Sankyo: Consultancy; Genentech, Inc.: Consultancy, Honoraria, Research Funding; Bayer: Consultancy, Honoraria, Research Funding; Merck: Consultancy; Teva: Consultancy; TG Therapeutics: Consultancy, Honoraria; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria; GlaxoSmithKline: Honoraria, Research Funding; Seattle Genetics: Consultancy, Honoraria, Research Funding; Memorial Sloan Kettering Cancer Center: Current Employment; IGM Biosciences: Research Funding; Pharmacyclics: Honoraria, Research Funding; Rocket Medical: Consultancy, Research Funding; ImmunoVaccine Technologies: Consultancy, Honoraria, Research Funding. Canales: Takeda: Consultancy, Honoraria, Speakers Bureau; Incyte: Consultancy; Sandoz: Honoraria, Speakers Bureau; iQone: Honoraria; Sanofi: Consultancy; Novartis: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria; Eusa Pharma: Consultancy, Honoraria; Celgene/Bristol-Myers Squibb: Consultancy, Honoraria; Gilead/Kite: Consultancy, Honoraria; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau. Fay: St Vincent's Hosptial, Sydney, Australia: Current Employment. Cheah: BMS: Consultancy, Research Funding; Abbvie: Research Funding; Janssen: Consultancy, Honoraria; MSD: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Ascentage Pharma: Consultancy, Honoraria; AstraZeneca: Consultancy, Honoraria; Lilly: Consultancy, Honoraria; TG therapeutics: Consultancy, Honoraria; Beigene: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Roche: Consultancy, Honoraria, Other: travel, Research Funding. Marlton: BeiGene: Honoraria, Membership on an entity's Board of Directors or advisory committees; F. Hoffmann-La Roche Ltd: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Queensland Health: Current Employment; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees. Wiebking: Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company; F. Hoffmann-La Roche Ltd: Current equity holder in publicly-traded company. Yin: Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months. To: Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company. Li: Genentech, Inc.: Current Employment, Current holder of individual stocks in a privately-held company. Huang: F. Hoffmann-La Roche Ltd: Current Employment. Zhou: Fibrogen China: Ended employment in the past 24 months; Roche Pharma Product Development: Current Employment. Penuel: Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company. O'Hear: Genentech, Inc.: Current Employment; F. Hoffmann-La Roche Ltd: Current holder of individual stocks in a privately-held company. Sehn: Novartis: Consultancy; Debiopharm: Consultancy; Genmab: Consultancy. OffLabel Disclosure: Mosunetuzumab is a CD20xCD3 bispecific antibody that redirects T cells to engage and eliminate malignant B cells. Mosunetuzumab is an investigational agent.

Introduction: Despite the curative intent of the R-CHOP regimen in the first-line treatment of diffuse large B-cell lymphoma (DLBCL), 35-40% of patients who received R-CHOP will eventually succumb to their disease (Coiffier, et al. Blood 2010; Sarkozy and Sehn. Ann Lymphoma 2019). As such, improved treatments are needed. Mosunetuzumab (Mosun) is a T-cell-engaging bispecific antibody that redirects T cells to eliminate malignant B cells by binding to CD3 on T cells and CD20 on B cells. Mosun monotherapy has a manageable safety profile and promising efficacy, including durable complete responses (CR), in patients (pts) with relapsed and/or refractory (R/R) non-Hodgkin lymphoma (NHL) (Schuster, et al. ASH 2019). This is the first report describing the safety and efficacy of Mosun plus CHOP (M-CHOP) in pts with R/R NHL and newly diagnosed DLBCL in the ongoing GO40515 (NCT03677141) study. Methods: Pts with R/R NHL and with newly diagnosed DLBCL received six 21-day cycles of M-CHOP. In Cycle (C) 1, Mosun was administered in step-up doses on Day (D) 1 (1mg), D8 (2mg), and D15 (13.5mg and 30mg in R/R NHL; 30mg in newly diagnosed DLBCL) to mitigate cytokine release syndrome (CRS). Full dose Mosun (C1D15 dose) was given on D1 of subsequent cycles in addition to CHOP. Interim and primary response assessments were obtained after C4 and C6, respectively. Primary prophylaxis with granulocyte colony-stimulating factor was mandatory for all pts. Pts with a partial response or stable disease at the end of C6 could continue Mosun monotherapy for up to 11 additional cycles. Response rates were based on the Lugano criteria (Cheson, et al. J Clin Oncol 2014). Results: As of June 3, 2020, 43 pts had received M-CHOP: seven patients with R/R NHL, and 36 pts with newly diagnosed DLBCL. Pts with disease stage II-IV were enrolled, with a median IPI score of 3 (range: 2-4) and ECOG performance status between 0 and 2. Median age was 66 (range: 39-87) and 17 pts (42%) were female. In pts with R/R NHL treated with M-CHOP (n=7), the overall response rate (ORR) was 86%, with 71% of pts achieving a CR. Twenty-seven out of 36 pts with previously untreated DLBCL started treatment at least three months prior to data cut-off date; in these pts the ORR was 96%, with a CR rate of 85% (Table). Grade (Gr) ≥3 adverse events (AEs) occurred in 37 pts (86%) and serious AEs in 19 pts (44%). Two pts (29%) with R/R NHL experienced CRS (one with Gr 1 and one with Gr 2; ASTCT grading, Lee et al. Biol Blood Marrow Transplant 2019); one pt received tocilizumab. Nineteen pts (53%) with previously untreated DLBCL had CRS events (14 with Gr 1, five with Gr2); one pt received tocilizumab. No pts required vasopressors or high-flow oxygen. All CRS events occurred in C1, resolved without sequelae, and did not result in discontinuation or delay in treatment. No immune effector cell-associated neurotoxicity syndrome (ICANS) events were observed. Neutropenia occurred in two pts with R/R NHL (29%; Gr 4 n=2) and 23 pts with newly diagnosed DLBCL (64%; Gr 3 n=3, Gr 4 n=20). Febrile neutropenia occurred in two pts (29%) with R/R NHL, and six pts (17%) with newly diagnosed DLBCL. Gr 5 AEs, excluding disease progression, were reported in two pts: one due to Pneumocystis jirovecii pneumonia in a pt with R/R NHL, and one due to pneumonia in a pt with newly diagnosed DLBCL. All pts with R/R NHL have completed treatment. Among pts with newly diagnosed DLBCL, four have completed treatment and 29 remain on treatment; one pt died on-study (Gr 5 pneumonia), and two withdrew from the study treatment due to AEs (one due to treatment-unrelated esophageal perforation; one due to treatment-related pneumonitis). Linear pharmacokinetics (PK) were observed for Mosun. No differences were seen in Mosun exposure for pts with R/R NHL and previously untreated DLBCL. Similar PK characteristics were seen with M-CHOP as with Mosun monotherapy, indicating no impact when co-administered with CHOP. Conclusions: Preliminary data show that Mosun, a novel CD20/CD3 bispecific antibody, when combined with CHOP confers high response rates and a manageable safety profile in pts with R/R NHL and previously untreated DLBCL. End of treatment response rate data for pts with previously untreated DLBCL, and correlative studies of T-cell response, will be presented. Disclosures Phillips: Incyte: Consultancy, Other: travel expenses; AstraZeneca: Consultancy; Seattle Genetics: Consultancy; Bayer: Consultancy, Research Funding; Abbvie: Consultancy, Research Funding; Pharmacyclics: Consultancy; Cardinal Health: Consultancy; BMS: Consultancy; Beigene: Consultancy; Karyopharm: Consultancy. Olszewski:TG Therapeutics: Research Funding; Adaptive Biotechnologies: Research Funding; Spectrum Pharmaceuticals: Research Funding; Genentech, Inc.: Research Funding. Munoz:Alexion: Consultancy; Portola: Research Funding; Janssen: Consultancy, Research Funding, Speakers Bureau; Kite, a Gilead Company: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy; Bayer: Consultancy, Research Funding, Speakers Bureau; Kyowa: Consultancy, Honoraria, Speakers Bureau; Seattle Genetics: Consultancy, Honoraria, Research Funding, Speakers Bureau; Pharmacyclics: Consultancy, Research Funding, Speakers Bureau; Verastem: Speakers Bureau; Juno/Celgene/BMS: Consultancy, Research Funding, Speakers Bureau; Beigene: Consultancy, Speakers Bureau; Fosunkite: Consultancy; Innovent: Consultancy; Acrotech/Aurobindo: Speakers Bureau; AstraZeneca: Speakers Bureau; Genentech/Roche: Research Funding, Speakers Bureau; AbbVie: Consultancy, Speakers Bureau; Merck: Research Funding; Incyte: Research Funding; Millenium: Research Funding. Kim:AstraZeneca: Consultancy; Novartis: Consultancy; Takeda: Consultancy; Sanofi: Consultancy; F. Hoffmann-La Roche Ltd/Genentech, Inc.: Consultancy; Voronoi: Consultancy; Boryung: Consultancy; AstraZeneca and Korea Health Industry Development Institute: Research Funding. Yoon:Celltrion: Honoraria; Samyang: Research Funding; Amgen, Chongkundang, Celgene, Astrazeneca: Consultancy. Greil:Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding; Abbvie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding; MSD Merck: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding; BMS/celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding; Daiichi Sankyo, Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding; Astra zeneca: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, accomodations, expenses, Research Funding. Westin:Novartis: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; Curis: Consultancy, Research Funding; Morphosys: Consultancy, Research Funding; 47: Research Funding; Janssen: Consultancy, Research Funding; Amgen: Consultancy; Kite: Consultancy, Research Funding; Astra Zeneca: Consultancy, Research Funding; BMS: Consultancy, Research Funding. Jaeger:Novartis: Consultancy, Honoraria, Research Funding; Amgen: Honoraria; Infinity: Honoraria; BMS/Celgene: Consultancy, Honoraria, Research Funding; True North: Honoraria, Research Funding; Miltenyi: Consultancy, Honoraria; CDR Life AG: Consultancy, Research Funding; Karyopharm: Honoraria; Gilead: Honoraria, Research Funding; Takeda: Honoraria; AbbVie: Honoraria; F. Hoffmann-La Roche: Honoraria, Research Funding. Canales:Celgene, Gilead, iQone, Janssen, Karyopharm, Novartis, F. Hoffmann-La Roche, Sandoz: Honoraria; Janssen, F. Hoffmann-La Roche, Sandoz, Takeda: Speakers Bureau. Chen:Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company; Bristol-Myer Squibb: Current equity holder in publicly-traded company, Ended employment in the past 24 months; Janssen Pharmaceuticals: Current equity holder in publicly-traded company. Althaus:Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company. O'Hear:Genentech, Inc.: Current Employment; F. Hoffmann-La Roche: Current equity holder in publicly-traded company. Negricea:F. Hoffmann-La Roche: Current Employment. Xie:F. Hoffmann-La Roche: Current Employment. McCord:Genentech, Inc.: Current Employment; F. Hoffman-La Roche: Current equity holder in publicly-traded company. Purev:Genentech, Inc.: Current Employment; F. Hoffmann-La Roche: Current equity holder in publicly-traded company. Vallurupalli:Received Research funding to University of Kansas to conduct the ongoing GO40515 clinical trial for which the abstract is being submitted.: Research Funding; On Kite speaker Bureau but do not receive any honorarium.: Speakers Bureau. OffLabel Disclosure: Mosunetuzumab (RG7828; CD20-TDB) 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: More effective, less toxic treatments with convenient administration are needed for patients (pts) with relapsed/refractory (R/R) B-cell lymphoma (B-NHL). Mosunetuzumab (Mosun) is a full-length, fully humanized IgG1 CD20/CD3 bispecific antibody that redirects T cells to engage and eliminate malignant B cells. In an ongoing Phase I/Ib study (GO29781; NCT02500407), Mosun has shown promising efficacy and tolerable safety in pts with R/R B-NHL when administered intravenously (IV) in step-up doses (Bartlett, et al. ASCO 2019, Schuster, et al. ASH 2019). Subcutaneous (SC) administration of Mosun is an alternative approach to minimize the risk of cytokine release syndrome (CRS), a key adverse event (AE) associated with T-cell engaging immunotherapies. Other potential benefits of SC dosing include reduced healthcare resource utilization and increased convenience. This is the first report of clinical data with Mosun SC in pts with R/R B-NHL. Methods: GO29781 is a Phase I/Ib, open-label, multicenter dose-escalation and expansion study of Mosun in R/R B-NHL. Pts included in this report received single-agent Mosun SC on Day 1 of each 21-day Cycle (Q3W), for 8 cycles in pts with complete response (CR) and up to 17 cycles in pts with partial response or stable disease. Dose escalation used a standard 3+3 design; doses from 1.6-20 mg were assessed. Key outcome measures included best objective response (per Cheson 2007 criteria), tolerability and maximum tolerated dose (MTD). Results: As of January 21 2020, 23 pts had received Mosun SC (diffuse large B-cell lymphoma, n=10; follicular lymphoma [FL], n=5; marginal-zone lymphoma [MZL], n=3; primary mediastinal large B-cell lymphoma, n=2; transformed [tr] FL, n=1; trMZL, n=1; tr nodular lymphocyte-predominant Hodgkin lymphoma, n=1). Median prior systemic therapies was 4 (range: 1-8); five pts (22%) had received prior chimeric antigen receptor T-cell therapy. Thirteen pts (57%) were refractory to last prior therapy and 16 (70%) were refractory to prior anti-CD20 therapy. The MTD was not reached. One dose-limiting toxicity (Grade [Gr] 4 neutropenia; resolved) was observed at dose 1.6mg. Among the 23 safety-evaluable pts, 22 (96%) experienced ≥1 AE; no AEs led to treatment discontinuation. Common (>20%) AEs related to Mosun SC were CRS (n=8, 35%), headache (n=5, 22%; all Gr 1) and injection site reaction (n=5, 22%; all Gr 1). All CRS events, graded by Lee criteria (Lee, et al. Blood 2014), occurred during Cycle 1 and were Gr 1 (n=6, 26%) or Gr 2 (n=2, 9%). In contrast to the Q3W fixed-dosing IV cohort, where 15% of pts experienced Gr 2 CRS at doses 0.05-2.8mg, no Gr 2 CRS occurred in the SC cohort at doses Among the 22 efficacy-evaluable pts across all dose levels, overall response rates and CR rates were 86% (6/7) and 29% (2/7) in indolent NHL pts and 60% (9/15) and 20% (3/15) in aggressive NHL pts, respectively. After a median 6.9 months (range: 1.3-22.1) on study for all SC pts, all but one CR pt remained in remission at the cut-off date. The pharmacokinetic (PK) profile of Mosun SC is characterized by a slow absorption rate (observed Tmax at 72 hours post-dose and Cmax reduced by ~70% versus IV) and high bioavailability (>75%), supporting the use of SC dosing for CRS mitigation. Consistent with reduced CRS, lower peak IL-6 levels were observed with SC dosing, with delayed onset versus Mosun IV. Conclusions: Mosun SC demonstrated a manageable safety profile, encouraging efficacy and a favorable PK profile in heavily pretreated R/R B-NHL pts. CRS events seen in Cycle 1 were mild, transient and required minimal intervention and no Gr ≥3 CRS events were reported. Notably, less frequent Gr 2 CRS events were observed with Mosun SC at 7-fold higher dose levels versus the IV fixed-dosing group. These results support continued dose escalation and optimization of Mosun SC in R/R B-NHL. Updated clinical, PK and biomarker data, including approximately 20 additional pts from an interim expansion cohort, will be presented. Disclosures Matasar: Genentech, Inc.: Consultancy, Honoraria, Research Funding; Daiichi Sankyo: Consultancy; GlaxoSmithKline: Honoraria, Research Funding; IGM Biosciences: Research Funding; Janssen: Honoraria, Research Funding; Pharmacyclics: Honoraria, Research Funding; Immunovaccine Technologies: Honoraria, Research Funding; Merck: Consultancy; Bayer: Consultancy, Honoraria, Research Funding; Juno Therapeutics: Consultancy; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Teva: Consultancy; Rocket Medical: Consultancy, Research Funding; Seattle Genetics: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria. 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. Yoon:Celltrion: Honoraria; Samyang: Research Funding; Amgen, Chongkundang, Celgene, Astrazeneca: Consultancy. Assouline:Takeda: Research Funding; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Speakers Bureau; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; AbbVie: Consultancy, Honoraria, Speakers Bureau; Pfizer: Consultancy, Honoraria; BeiGene: Consultancy, Honoraria, Research Funding. Bartlett:ADC Therapeutics: Consultancy; Kite, a Gilead Company: Research Funding; Immune Design: Research Funding; Janssen: Research Funding; Forty Seven: Research Funding; BMS/Celgene: Research Funding; Autolus: Research Funding; Merck: Research Funding; Millennium: Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pharmacyclics: Research Funding; Seattle Genetics: Consultancy, Research Funding; Roche/Genentech: Consultancy, Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; BTG: Consultancy; Acerta: Consultancy; Affimed Therapeutics: Research Funding. Ku:F. Hoffmann-La Roche: Honoraria. Giri:Royal Adelaide Hospital: Current Employment. Johnston:MSD: Membership on an entity's Board of Directors or advisory committees; F. Hoffmann-La Roche: Membership on an entity's Board of Directors or advisory committees. Flinn:Loxo: Research Funding; Unum Therapeutics: Consultancy, Research Funding; Incyte: Research Funding; BeiGene: Consultancy, Research Funding; Gilead Sciences: Consultancy, Research Funding; MorphoSys: Consultancy, Research Funding; Juno Therapeutics: Consultancy, Research Funding; Nurix Therapeutics: Consultancy; Acerta Pharma: Research Funding; Calithera Biosciences: Research Funding; Celgene: Research Funding; TG Therapeutics: Consultancy, Research Funding; Forma Therapeutics: Research Funding; Novartis: Research Funding; Constellation Pharmaceuticals: Research Funding; Great Point Partners: Consultancy; Genentech, Inc.: Research Funding; IGM Biosciences: Research Funding; Agios: Research Funding; Curio Science: Consultancy; Infinity Pharmaceuticals: Research Funding; Trillium Therapeutics: Research Funding; Pfizer: Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy, Research Funding; Teva: Research Funding; Seattle Genetics: Consultancy, Research Funding; Portola Pharmaceuticals: Research Funding; ArQule: Research Funding; Takeda: Consultancy, Research Funding; Merck: Research Funding; Curis: Research Funding; AbbVie: Consultancy, Research Funding; Iksuda Therapeutics: Consultancy; Janssen: Consultancy, Research Funding; AstraZeneca: Consultancy, Research Funding; Karyopharm Therapeutics: Research Funding; Kite Pharma: Consultancy, Research Funding; Forty Seven: Research Funding; Triphase Research & Development Corp.: Research Funding; Verastem: Consultancy, Research Funding; Yingli Pharmaceuticals ≠: Consultancy, Research Funding; Rhizen Pharmaceuticals: Research Funding; Johnson & Johnson: Other; Roche: Consultancy, Research Funding; Vincera Pharma: Consultancy; F. Hoffmann-La Roche: Research Funding. Goy:Celgene: Honoraria, Research Funding; Constellation: Research Funding; AbbVie: Research Funding; Hackensack UMC and University of Nebraska: Research Funding; AstraZeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: leadership role, Research Funding; RCCA/OMI: Current Employment; Janssen: Consultancy, Honoraria, Other: leadership role, Research Funding; Regional Cancer Care Associates/OMI: Current Employment; Infinity Verastem: Research Funding; MD Anderson: Research Funding; Kite, a Gilead Company: Consultancy, Current equity holder in publicly-traded company, Honoraria, Other: leadership role, Research Funding; Bayer: Research Funding; CALBG: Research Funding; PracticeUpdate Oncology: Consultancy; Infinity: Research Funding; Karyopharm: Research Funding; Genentech/Roche: Research Funding; Morphosys: Research Funding; Acerta: Consultancy, Honoraria, Other: leadership role, Research Funding; Xcenda: Consultancy; COTA: Consultancy, Current equity holder in publicly-traded company, Other: leadership role. Tzachanis:Fate: Research Funding; Incyte: Research Funding; Genetech: Research Funding; BMS: Research Funding; Takeda: Consultancy, Speakers Bureau; EUSA Pharma: Consultancy; Jazz: Consultancy; Magenta: Consultancy; Kyowa Kirin: Consultancy; Gilead Sciences: Consultancy, Research Funding, Speakers Bureau. O'Hear: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. To:Genentech, Inc.: Current Employment. Sarouei:Genentech, Inc.: Current Employment, Current equity holder in publicly-traded company. Li:F. Hoffmann-La Roche: Current Employment, Current equity holder in publicly-traded company; Genentech, Inc.: Current Employment. Bender:Genentech, Inc.: Current Employment, Current equity holder in private company. Penuel:F. Hoffmann-La Roche: Current equity holder in publicly-traded company; Genentech, Inc./ F. Hoffmann-La Roche: Current Employment. 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.

Objective Patients with advanced/recurrent epithelial ovarian and uterine cancers have limited treatment options beyond platinum chemotherapy. Both tumor types can express programmed death-ligand 1 (PD-L1), providing a potential therapeutic target for these patients. Here we present data from the ovarian and uterine cancer cohorts of the Phase I atezolizumab monotherapy study (PCD4989g). Methods This Phase I, multi-center, first-in-human, open-label, dose-escalation/expansion clinical trial investigated single-agent atezolizumab in cohorts of patients with recurrent epithelial ovarian or uterine cancer. The primary objective was to evaluate the safety and tolerability of single-agent atezolizumab. Anti-tumor activity and preliminary assessment of potential biomarkers were evaluated as secondary and exploratory objectives, respectively. Results The ovarian and uterine cancer cohorts enrolled 12 and 15 patients, respectively (10 [83%] and 5 [33%], respectively, had PD-L1 ≥ 5% on tumor-infiltrating immune cells). Atezolizumab was generally well tolerated with no new safety signals identified. The safety profiles in both cohorts were consistent with the known profile of atezolizumab monotherapy. Treatment-related adverse events (AEs) were mostly Grade ≤ 2, with no treatment-related Grade ≥ 4 AEs reported. Preliminary anti-tumor activity, with long durations of response, was observed in 2 patients from each cohort (ovarian cancer, 8.1 and 30.6+ months; uterine cancer, 7.3 and 16.6+ months). High microsatellite instability and tumor mutational burden were noted in the responders from the uterine cancer cohort. Conclusions Atezolizumab monotherapy was well tolerated in patients with epithelial ovarian or uterine cancer and may have clinical activity warranting further investigation. Trial registration ClinicalTrials.gov identifier: NCT01375842

7520 Background: Mosunetuzumab (M), a full-length, humanized, IgG1 bispecific antibody targeting CD20 and CD3, has shown promising efficacy and safety as monotherapy for R/R B-NHL (NCT02500407; Assouline, et al. ASH 2020). The combination of M with the anti-CD79b antibody-drug conjugate, Pola, showed synergistic anti-lymphoma activity in a mouse xenograft model. These data supported a Phase Ib/II, open-label, multicenter trial of M-Pola for R/R B-NHL (GO40516, NCT03671018). Here we present early clinical data from the Phase Ib cohort. Methods: Pts with R/R follicular lymphoma (FL, grade [Gr] 1–3a) or aggressive NHL (aNHL), including de novo diffuse large B-cell lymphoma (DLBCL), transformed FL (trFL) and FL Gr 3b (FL3b), received Cycle (C) 1 step-up doses of M on Day (D) 1 (1mg) and D8 (2mg), the target dose on C1D15, then continued at the target dose on C2D1 onwards. M was given every 21 days for eight cycles (or 17 cycles if stable disease or a partial response after C8). Pola (1.8mg/kg) was given with M on D1 of each cycle for six cycles. Results: As of November 17, 2020, 22 pts had received M-Pola (M target doses: 9mg, n=7; 20mg, n=3; 40mg, n=6; 60mg [with D1 dose of 30mg from C3 onwards], n=6). Pts had DLBCL (n=12), FL (n=3), FL3b (n=3) and trFL (n=4). Pt characteristics include: median age of 70 (38–81) years; median of 3 (1–10) prior lines of therapy; 7 (32%) pts had prior CAR-T therapy; 17 (77%) and 19 (86%) pts had disease refractory to last prior therapy and prior anti-CD20 therapy, respectively. Median follow-up duration was 9.6 (0.7–23.7) months. The most frequent treatment-related adverse events (AEs) were neutropenia (45.4%), fatigue, nausea and diarrhea (all 36.4%). Cytokine release syndrome (CRS) was observed in 2 pts (9.1%; both Gr 1 by ASTCT 2019 criteria). One dose-limiting toxicity (Gr 3 new onset atrial fibrillation) was observed in the 40mg cohort. The maximum tolerated dose was not exceeded. The most common Gr ≥3 and serious AEs were both neutropenia, observed in 8 (36.4%) and 3 (13.6%) pts, respectively. Two (9.3%) Gr 5 AEs occurred: sudden cardiac death (n=1) and respiratory failure (n=1); neither was deemed treatment related. No immune effector cell-associated neurotoxicity was observed. The Table shows preliminary efficacy data. Preliminary efficacy in the dose-escalation cohort. Conclusions: These data indicate that M-Pola has an acceptable safety profile, with no Gr ≥2 CRS observed, and promising efficacy in pts with R/R NHL with predominantly aggressive disease. The Phase II expansion cohort in R/R DLBCL is ongoing, with no mandatory hospitalization required. Clinical trial information: NCT03671018. [Table: see text]

Background Programmed death-ligand 1 (PD-L1) protein is expressed in various cancers, including small-cell lung cancer (SCLC). Atezolizumab inhibits PD-L1 signaling, thus restoring tumor-specific T-cell immunity. Here, we report results from the first-in-human phase 1 PCD4989g study ( NCT01375842 ) of atezolizumab, in a cohort of patients with relapsed/refractory SCLC. Patients and Methods Eligible patients with incurable or metastatic SCLC, which was advanced or recurrent since the last antitumor therapy, received atezolizumab 15 mg/kg or 1200 mg intravenously every 3 weeks for 16 cycles or until loss of clinical benefit. The primary endpoint was safety. Efficacy and biomarkers of antitumor activity were also assessed. Results Seventeen patients were enrolled. Any-grade and grade ≥3 treatment-related adverse events (TRAEs) occurred in 11 (64.7%) and 5 (29.4%) patients, respectively. The most common any-grade TRAE was fatigue (4 patients [23.5%]). Partial response to atezolizumab was achieved in 1 patient (5.9%) per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1), and 3 (17.6%) per immune-related response criteria (irRC). Durations of response were 2.8 to > 45.7 months. Median investigator-assessed progression-free survival (PFS) per RECIST v1.1 and irRC was 1.5 (95% confidence interval [CI], 1.2-2.7) and 2.9 (95% CI, 1.2-6.1) months, respectively. Median overall survival (OS) was 5.9 months (95% CI, 4.3-12.6). Patients with high (≥ median expression) T-effector gene signature and PD-L1 mRNA expression appeared to show a trend toward improved PFS (per irRC) and OS. Conclusion Atezolizumab was generally well tolerated and exhibited antitumor activity in a small cohort of patients with relapsed/refractory SCLC.

Purpose: Atezolizumab [anti–programmed death-ligand 1 (PD-L1)] selectively targets PD-L1 to block its interaction with receptors programmed death 1 and B7.1, thereby reinvigorating antitumor T-cell activity. We evaluated the long-term safety and activity of atezolizumab, along with biological correlates of clinical activity endpoints, in a cohort of patients with melanoma in an ongoing phase Ia study (NCT01375842). Patients and Methods: Patients with unresectable or metastatic melanoma were enrolled to receive atezolizumab 0.1 to 20 mg/kg or ≥10 mg/kg every 3 weeks. Primary study objectives were safety and tolerability. Secondary objectives included investigator-assessed efficacy measures; pharmacodynamic and predictive biomarkers of antitumor activity were explored. Results: Forty-five patients were enrolled and were evaluable for safety. Most treatment-related adverse events (AE) were grade 1/2 (60%). Fatigue (44%), pruritus (20%), pyrexia (18%), and rash (18%) were the most common treatment-related AEs of any grade. No treatment-related deaths occurred. Overall response rate was 30% among 43 efficacy- evaluable patients, with a median duration of response of 62 months [95% CI, 35–not estimable (NE)]. Clinically meaningful long-term survival was observed, with a median overall survival of 23 months (95% CI, 9–66). Baseline biomarkers of tumor immunity [PD-L1 expression on immune cells, T effector (Teff), and antigen presentation gene signatures) and tumor mutational burden (TMB) were associated with improved response, progression-free survival, and overall survival. Conclusions: Atezolizumab was well tolerated, with durable responses and survival in patients with melanoma. PD-L1 expression, TMB, and Teff signatures may indicate improved benefit with atezolizumab in these patients.

Importance Atezolizumab (anti–programmed cell death ligand 1 [PD-L1]) is well tolerated and clinically active in multiple cancer types. Its safety and clinical activity in metastatic triple-negative breast cancer (mTNBC) has not been reported. Objective To evaluate the safety, clinical activity, and biomarkers associated with the use of single-agent atezolizumab in patients with mTNBC. Design, Setting, and Participants Women with mTNBC (defined by investigator assessment) were enrolled between January 2013 and February 2016 in a multicohort open-label, phase 1 study at US and European academic medical centers. Median follow-up was 25.3 months (range, 0.4-45.6 months). Eligible patients regardless of line of therapy had measurable disease by Response Evaluation Criteria in Solid Tumors, version 1.1; Eastern Cooperative Oncology Group performance status of 0 to 1; and a representative tumor sample for assessment of immune cell (IC) PD-L1 expression. Interventions Atezolizumab was given intravenously every 3 weeks until unacceptable toxic effects or loss of clinical benefit. Main Outcomes and Measures Primary outcome was safety and tolerability. Activity and exploratory outcomes included objective response rate (ORR), duration of response, progression-free survival (PFS), and overall survival (OS). Outcomes were assessed in all patients and in key patient subgroups. Results Among 116 evaluable patients (median age, 53 years [range, 29-82 years]), treatment-related adverse events occurred in 73 (63%); 58 (79%) were grade 1 to 2. Most adverse events occurred within the first treatment year. The ORRs were numerically higher in first-line (5 of 21 [24%]) than in second-line or greater patients (6 of 94 [6%]). Median duration of response was 21 months (range, 3 to ≥38 months). Median PFS was 1.4 (95% CI, 1.3-1.6) months by RECIST and 1.9 (95% CI, 1.4-2.5) months by irRC. In first-line patients, median OS was 17.6 months (95% CI, 10.2 months to not estimable). Patients with PD-L1 expression of at least 1% tumor-infiltrating ICs had higher ORRs and longer OS (12% [11 of 91]; 10.1 [95% CI, 7.0-13.8] months, respectively) than those with less than 1% ICs (0 of 21; 6.0 [95% CI, 2.6-12.6] months, respectively). High levels of ICs (>10%) were independently associated with higher ORRs and longer OS. Conclusions and Relevance Single-agent atezolizumab was well tolerated and provided durable clinical benefit in patients with mTNBC with stable or responding disease and in earlier lines of treatment. Trial Registration ClinicalTrials.gov identifier:NCT01375842

Importance Atezolizumab (anti–programmed death ligand 1) has demonstrated safety and activity in advanced and metastatic urothelial carcinoma, but its long-term clinical profile remains unknown. Objective To report long-term clinical outcomes with atezolizumab therapy for patients with metastatic urothelial carcinoma. Design, Setting, and Participants Patients were enrolled in an expansion cohort of an ongoing, open-label, phase 1 study. Median follow-up was 37.8 months (range, >0.7 to 44.4 months). Enrollment occurred between March 2013 and August 2015 at US and European academic medical centers. Eligible patients had measurable disease per Response Evaluation Criteria in Solid Tumors version 1.1, Eastern Cooperative Oncology Group performance status 0 to 1, and a representative tumor sample. Programmed death ligand 1 expression on immune cells was assessed (VENTANA SP142 assay). Interventions Atezolizumab was given intravenously every 3 weeks until unacceptable toxic effects, protocol nonadherence, or loss of clinical benefit. Main Outcomes and Measures Primary outcome was safety. Secondary outcomes included objective response rate, duration of response, and progression-free survival. Response and overall survival were assessed in key baseline subgroups. Results Ninety-five patients were evaluable (72 [76%] male; median age, 66 years [range, 36-89 years]). Forty-five (47%) received atezolizumab as third-line therapy or greater. Nine patients (9%) had a grade 3 to 4 treatment-related adverse event, mostly within the first treatment year; no serious related adverse events were observed thereafter. One patient (1%) discontinued treatment due to a related event. No treatment-related deaths occurred. Responses occurred in 26% (95% CI, 18%-36%) of patients. Median duration of response was 22.1 months (range, 2.8 to >41.0 months), and median progression-free survival was 2.7 months (95% CI, 1.4-4.3 months). Median overall survival was 10.1 months (95% CI, 7.3-17.0 months); 3-year OS rate was 27% (95% CI, 17%-36%). Response occurred in 40% (95% CI, 26%-55%; n = 40) and 11% (95% CI, 4%-25%; n = 44) of patients with programmed death ligand 1 expression of at least 5% tumor-infiltrating immune cells (IC2/3) or less than 5% (IC0/1), respectively. Median overall survival in patients with IC2/3 and IC0/1 was 14.6 months (95% CI, 9.0 months to not estimable) and 7.6 months (95% CI, 4.7 to 13.9 months), respectively. Conclusions and Relevance Atezolizumab remained well tolerated and provided durable clinical benefit to a heavily pretreated metastatic urothelial carcinoma population in this long-term study. Trial Registration clinicaltrials.gov Identifier:NCT01375842

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: Improved treatments are needed for relapsed or refractory (R/R) non-Hodgkin lymphoma (NHL) pts. Options are particularly limited for pts with B-cell NHLs who are R/R to CAR-T therapies or for whom a delay in effective therapy precludes this approach. 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). In an ongoing Phase I/Ib study (GO29781; NCT02500407), promising efficacy and favorable tolerability were observed in R/R NHL pts (Budde et al. ASH 2018; Bartlett et al. ASCO 2019). We report complete remissions (CRs) with M in NHL pts who are R/R to CAR-T therapy, as well as activity with M re-treatment. Methods: GO29781 is an open-label, multicenter, Phase I/Ib, dose escalation and expansion study of M in R/R B-cell NHL. Data is presented from Group B, in which M is administered with step-up dosing on Days 1, 8, and 15 of Cycle 1, and then as a fixed dose on Day 1 of each subsequent 21-day cycle (maximum 17 cycles). Outcome measures include best objective response rate (ORR) by revised International Working Group criteria, maximum tolerated dose (MTD), and tolerability. Results: As of June 4, 2019, 218 pts in Group B had received any amount of M. Indolent NHL (iNHL) pts (n=72) were mainly follicular lymphoma (FL, n=69). Aggressive NHL (aNHL) pts (n=141) were mainly diffuse large B-cell lymphoma (DLBCL, n=87) or transformed FL (trFL, n=29). Median prior systemic therapies was 3 (range: 1-14). Twenty-three pts had prior CAR-T therapy (12 DLBCL, 6 trFL, 5 FL), and 16 were efficacy evaluable (7 DLBCL, 5 trFL, 4 FL). ORR and CR rates were 43.8% (7/16) and 25.0% (4/16, 2 DLBCL and 2 FL), respectively. Expansion of previously administered CAR-Ts after M administration was detected by quantitative PCR, in line with the mechanism of action of M. Dose escalation is ongoing, supported by a positive exposure-response relationship for efficacy and broad therapeutic window with step-up dosing (Li et al. ASH 2019). Among efficacy-evaluable pts across all dose levels, ORR and CR rates were 64.1% (41/64) and 42.2% (27/64) in iNHL pts and 34.7% (41/119) and 18.6% (22/119) in aNHL pts, respectively. CRs appeared durable, with 25/27 (92.6%) iNHL pts (median time from first CR: 5.8 months; range: 0.2-28.9) and 15/22 (68.2%) aNHL pts (median time from first CR: 8.8 months; range: 0.0-25.4) who achieved CR remaining in remission. Re-treatment with M was allowed in CR pts who relapsed. Four pts, including 1 in Group A who was initially treated with a fixed, non-step-up dosing schedule, received M re-treatment. One CR and 2 partial responses were observed. All three responses are ongoing, with the CR pt in second remission for 314 days. The MTD of M has not been reached at doses up to 1/2/60mg (Cycle 1 Day 1, 8, and 15). Adverse events (AEs) leading to treatment withdrawal were uncommon (12/218, 5.5%). Cytokine release syndrome (CRS), graded by Lee criteria (Lee et al. Blood 2014;124:188-95), was observed in 28.4% of pts, and was mostly Grade (Gr) 1 (21.1%) or Gr 2 (6.0%); Gr 3 CRS occurred in 1.4% of pts. Most CRS events occurred in Cycle 1; 5 pts (2.7%) had CRS during or after Cycle 2. Three of 218 pts (1.4%) received tocilizumab for CRS management; all 3 events resolved without sequelae (for 1 pt, CRS resolved after the cutoff date). Neurological AEs (NAEs) were reported in 44% of pts (Gr 1, 28.0%; Gr 2, 12.8%; Gr 3, 3.2%). Common NAEs were headache (14.7%), insomnia (10.1%), and dizziness (9.2%). Potential immune effector cell-associated neurotoxicity syndrome (ICANS)-like NAEs of Gr 1 or Gr 2 confusional state occurred in 3 pts (1.4%) during cycles 1 and 2. The frequency of CRS and NAEs did not correlate with M exposure, likely due to step-up dosing, which effectively mitigates acute toxicities and allows administration of higher doses (Bartlett et al. ASCO 2019; Li et al. ASH 2019). Among the 4 pts who were re-treated with M, no CRS was observed and NAEs were reported in 1 pt (Gr 1 headache and insomnia). Among the 23 pts who were R/R to CAR-T therapy, CRS occurred in 5 pts (21.7%; Gr 1, 13.0%; Gr 2, 4.3%; Gr 3, 4.3%) and NAEs in 8 pts (34.8%; Gr 1, 17.4%; Gr 2, 13.0%; Gr 3, 4.3%), with no ICANS-like events. Conclusions: M has favorable tolerability and durable efficacy in pts with heavily pre-treated R/R B-cell NHL, including CRs in pts with disease progression after CAR-T therapies. Preliminary data support the possibility for re-treatment with M. Disclosures Schuster: Novartis: Honoraria, Patents & Royalties: Combination CAR-T and PD-1 Inhibitors, Research Funding; Nordic Nanovector: Consultancy, Honoraria; AstraZeneca: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria, Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Acerta: Consultancy, Honoraria, Research Funding; Gilead: Consultancy, Honoraria, Research Funding; Loxo Oncology: Consultancy, Honoraria; Merck: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria; Genentech: Consultancy, Honoraria, Research Funding. Bartlett:Bristol-Myers Squibb: Research Funding; Celgene: Research Funding; Kite Pharma: Research Funding; Merck: Research Funding; Millennium: Research Funding; Pfizer: Research Funding; Pharmacyclics: Research Funding; Gilead: Research Funding; Immune Design: Research Funding; Incyte: Research Funding; Janssen: Research Funding; ADC Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Affimed: Research Funding; Autolus: Research Funding; Forty Seven: Research Funding; Genentech, Inc.: Research Funding. Assouline:Janssen: Consultancy, Honoraria, Speakers Bureau; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria, Speakers Bureau. Yoon:Kyowa Hako Kirin: Research Funding; Genentech, Inc.: Research Funding; Novartis: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; MSD: Consultancy; Janssen: Consultancy; Yuhan Pharma: Research Funding. Bosch:Kyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Acerta: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Honoraria, Research Funding; AstraZeneca: Honoraria, Research Funding; F. Hoffmann-La Roche Ltd/Genentech, Inc.: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Sehn:Acerta: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; F. Hoffmann-La Roche/Genentech: Consultancy, Honoraria, Research Funding; Lundbeck: Consultancy, Honoraria; Kite Pharma: Consultancy, Honoraria; Lundbeck: Consultancy, Honoraria; Morphosys: Consultancy, Honoraria; F. Hoffmann-La Roche/Genentech: Consultancy, Honoraria, Research Funding; Apobiologix: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Kite Pharma: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Verastem: Consultancy, Honoraria; Merck: Consultancy, Honoraria; Merck: Consultancy, Honoraria; TG Therapeutics: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; Karyopharm: Consultancy, Honoraria; Morphosys: Consultancy, Honoraria; Abbvie: Consultancy, Honoraria; TEVA Pharmaceuticals Industries: Consultancy, Honoraria; Acerta: Consultancy, Honoraria; Janssen-Ortho: Consultancy, Honoraria; Janssen-Ortho: Honoraria; TG Therapeutics: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Astra Zeneca: Consultancy, Honoraria; TEVA Pharmaceuticals Industries: Consultancy, Honoraria; Astra Zeneca: Consultancy, Honoraria. Cheah:Janssen: Honoraria; Acerta: Honoraria; F. Hoffmann-La Roche Ltd: Honoraria, Research Funding; AbbVie: Research Funding; Celgene: Research Funding; Gilead: Honoraria; Loxo: Honoraria. Shadman:Mustang Biopharma: Research Funding; Gilead: Research Funding; AbbVIe: Consultancy, Research Funding; Genentech, Inc.: Consultancy, Research Funding; AstraZeneca: Consultancy; Sound Biologics: Consultancy; Pharmacyclics: Consultancy, Research Funding; ADC Therapeutics: Consultancy; Atara: Consultancy; Bigene: Research Funding; Celgene: Research Funding; TG Therapeutics: Research Funding; Verastem: Consultancy; Acerta: Research Funding; Emergent: Research Funding; Sunesis: Research Funding; Merck: Research Funding. Gregory:MSD: Other: grant pending, Research Funding; Beigene: Other: Grant pending, Research Funding; Celgene: Other: grant pending, Research Funding; Monash University: Research Funding; Roche: Speakers Bureau; Gilead: Membership on an entity's Board of Directors or advisory committees; AbbVie: Other: grant pending, Research Funding; Janssen: Other: grant pending, Research Funding; Melbourne Haematology: Consultancy, Honoraria, Other: Travel fees and conference support, Speakers Bureau. Wei:Genentech, Inc./F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Yin:Genentech, Inc: Employment, Equity Ownership. Kwan:Genentech, Inc: Employment, Equity Ownership. Yousefi:F. Hoffmann-La Roche Ltd: Employment. Hernandez: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. Budde:F. Hoffmann-La Roche Ltd: Consultancy. Off Label 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: Neurologic toxicities have resulted in restrictions in driving/engaging in hazardous occupations and activities for pts receiving marketed T-cell-engaging CD19-directed bispecific antibodies and chimeric antigen receptor T-cell (CAR-T) therapies. 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 trials investigating the safety and preliminary efficacy of M currently mandate a driving restriction for enrolled pts while receiving treatment. Data collected to date show that neurologic toxicities associated with M may be milder than for other CD19-directed therapies, which may be due in part to the step-up dosing regimens investigated (Budde et al. ASH 2018; Bartlett et al. ASCO 2019). We initiated a systematic review of neurologic adverse events (NAEs) in pts treated with M to characterize the nature of driving-impacting NAEs and to develop a more patient-centric approach to NAE risk-mitigation that would reduce the burden on pts in M clinical trials. Methods: A systematic review of NAEs observed in the ongoing Phase I/Ib study (GO29781; NCT02500407) of M in relapsed or refractory non-Hodgkin lymphoma (NHL) pts (n=205) was performed (data cutoff: Jan 31, 2019; median safety follow-up: 116 days). NAEs were defined as any AE reported as a Preferred Term (PT) within the System Organ Class (SOC) Nervous System Disorders and SOC Psychiatric Disorders, as recommended by FDA. NAEs were further classified by those that have impact on cognition and consciousness (CC-NAEs), and those that may impair driving (DI-CC-NAEs). In conjunction with an independent neurology consultant, DI-CC-NAEs were adjudicated based on medical judgement and determined a priori based on reported PTs. Univariate and multivariate logistic regression with a 5% significance level was performed to determine the association of demographic and disease characteristics with DI-CC-NAEs occurring in the first 3 cycles of M treatment, as 90% (27/30) of events occurred within this period. Results: NAEs were observed in 49% (100/205) of enrolled pts and were mostly grade (Gr) 1-2 (Gr 1, 69/205 [34%]; Gr 2, 24/205 [12%]). The most frequent NAEs were headache (32/205, 16%), dizziness (27/205, 13%), and insomnia (19/205, 9%). Gr ≥3 NAEs were rare (3%, all Gr 3) and occurred as clinical sequelae to non-NAEs (e.g. Gr 3 hepatic encephalopathy secondary to Gr 4 liver function test increased, Gr 3 seizure secondary to electrolyte disturbance, Gr 3 post-herpetic neuralgia). The majority of NAEs occurred early and were transient (median onset from first M infusion: 16 days; median duration: 10 days). Most resolved (11% were unresolved at time of data cut). Frequency of NAEs was not associated with M dose level (Figure) or exposure (Li et al. ASH 2019). At the time of data cut, 30 DI-CC-NAEs (Gr 1, 17/30 [57%]; Gr 2, 9/30 [30%]; Gr 3, 4/30 [13%]) were reported, including PTs of confusional state, delirium, disturbance in attention, encephalopathy, hallucination, memory impairment, and seizure. These events were observed in 24 (12%) pts, and were mostly Gr 1-2 (26/30, 87%). Three pts experienced four Gr 3 DI-CC-NAEs (confusional state, hepatic encephalopathy, encephalopathy, seizure). The majority of DI-CC-NAEs (67%) occurred in pts with aggressive NHL (aNHL) and who had elevated C-reactive protein (CRP) at baseline based on the local institutional upper limit of normal (sensitivity: 67%; specificity: 66%; positive predictive value: 23%; negative predictive value: 93%; Table). Other characteristics included in the multivariate analysis were age, sex, and tumor bulk, but these did not demonstrate association with occurrence of DI-CC-NAEs. Conclusion: Based on these analyses, the driving restriction that applied to all pts for the duration of M treatment was amended to a restriction covering the first 2 cycles only in a subset of pts who had aNHL and elevated CRP at baseline. This novel approach of individualized risk mitigation for driving based on in-depth assessment of NAEs allows for a more targeted and patient-centric mitigation strategy to optimize the protection of pts at risk, and is useful during clinical development when the safety profile is being characterized. As further data are accumulated, the multivariate analysis can be updated to further refine the pts at risk for DI-CC-NAE. Disclosures Diefenbach: Bristol-Myers Squibb: Consultancy, Research Funding; Denovo: Research Funding; Genentech: Consultancy, Research Funding; Incyte: Research Funding; LAM Therapeutics: Research Funding; MEI: Research Funding; Merck: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Millenium/Takeda: Research Funding; Trillium: Research Funding. Assouline:Abbvie: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Speakers Bureau; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria, Speakers Bureau. Bosch:Kyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Acerta: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Honoraria, Research Funding; F. Hoffmann-La Roche Ltd/Genentech, Inc.: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; AstraZeneca: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Cheah:F. Hoffmann-La Roche Ltd: Honoraria, Research Funding; AbbVie: Research Funding; Celgene: Research Funding; Gilead: Honoraria; Janssen: Honoraria; Acerta: Honoraria; Loxo: Honoraria. Kim:J + J: Research Funding; Novartis: Research Funding; Celltrion: Research Funding; Novartis: Research Funding; Donga: Research Funding; Kyowa-Kirin: Research Funding; F. Hoffmann-La Roche Ltd: Research Funding. Matasar:Merck: Consultancy, Equity Ownership; Genentech, Inc.: Consultancy, Honoraria, Other: Travel, accommodation, expenses , Research Funding; Bayer: Consultancy, Honoraria, Other; Roche: Consultancy, Honoraria, Other: Travel, accommodation, expenses , Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; GlaxoSmithKline: Honoraria, Research Funding; Daiichi Sankyo: Consultancy; Seattle Genetics: Consultancy, Honoraria, Other: Travel, accomodation, expenses, Research Funding; Rocket Medical: Consultancy, Research Funding; Teva: Consultancy; Bayer: Other: Travel, accommodation, expenses; Janssen: Honoraria, Research Funding; Juno Therapeutics: Consultancy. Panizo:Janssen: Speakers Bureau; Kyowa Kirin: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; F. Hoffmann-La Roche Ltd: Consultancy, Speakers Bureau. Yoon:F. Hoffmann-La Roche Ltd: Research Funding. Bender:Genentech, Inc.: Employment, Equity Ownership. Hernandez:Genentech, Inc.: Employment, Equity Ownership. Li:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. McCall:F. Hoffmann-La Roche Ltd: Equity Ownership; Genentech, Inc.: Employment, Equity Ownership. O'Hear:Genentech, Inc.: Employment; F. Hoffmann-La Roche Ltd: Equity Ownership. Wei:Genentech, Inc./F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Yin:Genentech, Inc: Employment, Equity Ownership. Yousefi:F. Hoffmann-La Roche Ltd: Employment. Kwan:Genentech, Inc: Employment, Equity Ownership. Nastoupil:Celgene: Honoraria, Research Funding; Bayer: Honoraria; Spectrum: Honoraria; Janssen: Honoraria, Research Funding; Genentech, Inc.: Honoraria, Research Funding; Novartis: Honoraria; TG Therapeutics: Honoraria, Research Funding; Gilead: Honoraria. 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.

Importance Checkpoint inhibition in cancer immunotherapy related to T-cell–driven mechanisms of action associated with acute macular neuroretinopathy (AMN) and diffuse retinal venulitis, an adverse event not previously described, is reported here. Objective To describe 2 patients who developed ophthalmologic events after treatment with the programmed death 1 axis inhibitor, atezolizumab. Design, Setting, and Participants Retrospective review of 2 patients treated with atezolizumab for metastatic breast cancer and colon cancer, respectively, who presented with AMN and diffuse retinal venulitis conducted at 2 tertiary medical centers. Main Outcomes and Measures Multimodal imaging including near infrared, optical coherence tomography, and fluorescein angiography were used to characterize retinal vascular abnormalities. Results Based on optical coherence tomography and multimodal imaging findings, the clinical diagnosis of AMN associated with diffuse retinal venulitis was made in these 2 patients receiving atezolizumab. Conclusions and Relevance While only 2 cases of patients receiving the programmed death ligand 1 inhibitor atezolizumab who experienced AMN and diffuse retinal venulitis are described here, these findings suggest that patients receiving programmed death 1 axis inhibitor therapies may need to be monitored for unexpected immune-related ocular toxicity including abnormalities of the microvasculature and large retinal vessels. Further studies might investigate the potential mechanisms of retinal vascular changes associated with these therapies.

Background: The PD-L1/PD-1 inhibitors activate the immune system both in the tumor microenvironment and peripheral blood. Here we investigated the relationship between peripheral immune system and clinical outcome of metastatic cancer patients treated with atezolizumab (anti-PDL1) across five tumor types. Methods: 426 patients with melanoma (n=45), non-small cell lung cancer (NSCLC, n=89), kidney cancer (RCC, n=72), triple-negative breast cancer (TNBC, n=116) and bladder cancer (UBC, n=104) were treated with atezolizumab in the phase I clinical trial PCD4989g (NCT01375842). Normal/abnormal blood neutrophils, monocytes, eosinophils, basophils and lymphocytes were measured by local laboratories, while T (CD3, CD4 and CD8), B (CD19), and NK (CD56) lymphocyte subsets were centrally analyzed by flow cytometry. Neutrophil:lymphocyte ratio (NLR) and relative lymphocyte counts (RLC) were also evaluated. Association of the immune cell subsets and clinical outcome (ORR, PFS and OS) was assessed in multivariate analyses considering liver metastases, LDH, line of therapy and ECOG performance status. Results: The prevalence of hematologic abnormalities across tumors was: lymphopenia (27-57%), followed by neutrophilia (2-24%), monocytosis (0-15%), eosinophilia (1-13%), eosinopenia (0-14%), basophilia (2-7%) and basopenia (0-6%). Neutrophilia, monocytosis, lymphopenia and low/high eosinophils were associated with worse PFS and OS, although with a different imprint depending on tumor ontogeny: neutrophilia was linked to reduced OS in melanoma and PFS for UBC, monocytosis was associated with lower OS in TNBC and UBC. Lymphopenia was associated with reduced PFS and OS in NSCLC, TNBC and reduced PFS in melanoma. NLR>=5 was associated with reduced PFS in melanoma, NSCLC, RCC, UBC and reduced OS in UBC, NSCLC and TNBC. RLC>=17.5% was linked to longer PFS in melanoma, RCC, UBC and to increased OS in TNBC, NSCLC and UBC. Lymphocyte subset analysis showed lymphopenia in B cells (40-61%), CD3 T cells (32-71%), CD4 T cells (28-66%), CD8 T cells (25-46%) and NK cells (16-23%). CD3 lymphopenia was associated to reduced OS in NSCLC, and CD4 lymphopenia was associated to reduced OS in NSCLC and TNBC. NK lymphopenia was associated to decreased OS and PFS in TNBC. Conclusion: This is the first study showing that higher pretreatment relative lymphocyte counts is associated to improved clinical outcome in patients from different tumor etiologies treated with atezolizumab. The association of peripheral T cell counts to improved outcome in some indications suggests that the local antitumor response may be linked to pre-existing systemic T cells. Citation Format: Yijin Li, Ching-Wei Chang, Marcella Fasso, Carol O'Hear, Priti S. Hegde, Luciana Molinero. Baseline blood lymphocytes are associated with improved clinical outcome in atezolizumab-treated patients across multiple indications [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 2616.

9009Background: Alectinib has proven systemic and CNS efficacy in patients (pts) with ALK+ aNSCLC (ALEX study). Tumor cell death caused by alectinib may release antigens broadening the potential an...