1188PD - Margetuximab (M) + pembrolizumab (P) for treatment of patients (pts) with HER2+ gastroesophageal adenocarcinoma (GEA) post-trastuzumab (T): Survival analysis

Abstract

BackgroundCurrent standard of care (SOC) in 2L GEA, ramucirumab + taxane, has median progression free survival (mPFS) of 4.4 months (m) and median overall survival (mOS) of 9.6 m. Chemotherapy-backbone HER2-targeted agents tested in 2L HER2+ GEA TyTAN and GATSBY studies showed mPFS and mOS ranged 2.4-5.4 months (m), and 7.1-11.2 m. P, in 2L KN061, showed mPFS and mOS of 1.5 m and 9.1 m in GEA pts with PD-L1 CPS >1, and both were lower for PD-L1 all-comers. M is an investigational anti-HER2 Fc-optimized monoclonal antibody that can coordinate activation between innate and adaptive immunity. In pts treated with M+P, we previously reported ORR of 33% in HER-2 IHC-3+ gastric cancer (GC) pts and over 50% in pts with HER-2+/PD-L1+ tumors. MethodsHER2+ PD-L1 unselected 2L GEA pts (N=86) were enrolled post progression on T-based therapy (tx) and treated with M (15mg/kg) and P (200mg) IV Q3wk. We report mPFS and mOS in the overall expansion cohort and in biomarker subgroups including archival PD-L1 and HER2 IHC, ERRB2 ctDNA (prior to 2L tx), and tumor site (GC vs junction [GEJ]). ResultsMedian duration of tx was 3.8 m (range 0.7-26.5), with median follow-up 11.3 m (range 1.6-28.6). Pt characteristics (n,%) included: GC 60 (70%), HER2 IHC3+ 68 (79%), PD-L1 CPS>1 32 (37%), ERBB2 ctDNA+ 46 (53%), and MSI-high 1 (1%). In overall GEA pts, mPFS was 3.5 m (95% CI 1.64-4.76), and mOS was 13.9 m (95% CI 9.26-16.82); OS rates at 6/12/18/24 m were 77/57/35/32%, respectively. In GEA HER2 IHC3+ pts, mPFS was 4.5 m (95%CI 2.7-7.5) and mOS was 16.8 m (95%CI 12.23-not reached (NR)). OS rates at 6/12/18/24 m were 85/66/48/44%, respectively; IHC3+ GC (54 [63%]) showed mPFS of 4.7 m (95% CI 2.73-7.49) and mOS NR (95% CI 12.25-NR). IHC3+/ctDNA+ confirmation GEA (38 [44%]) showed mPFS 7.5 m (95% CI 3.5-12.4) and mOS NR (13.27-NR), and IHC3+/ctDNA+ GC (31 [36%]) showed mPFS 5.6 m (95% CI 2.73-8.34) and mOS NR (12.48 – NR). Median PFS and mOS were lower in GEJ: 1.5 m (1.38, 4.34) and 9.2 m (5.26, 15.41), respectively. ConclusionsIn this study, M+P, a chemotherapy-free regimen, demonstrated acceptable tolerability in HER2+ GEA pts post-T, with extension of time-to-event endpoints compared to historical experience with SOC regimens, and checkpoint inhibitors alone. Clinical trial identificationNCT02689284. Legal entity responsible for the studyMacroGenics, Inc. FundingMacroGenics, Inc. DisclosureD.V. Catenacci: Honoraria (self), Advisory / Consultancy: Amgen; Honoraria (self), Advisory / Consultancy: Bristol-Myers Squibb; Honoraria (self): Five Prime Therapeutics; Honoraria (self), Speaker Bureau / Expert testimony: Foundation Medicine; Honoraria (self), Advisory / Consultancy: Genentech/Roche; Honoraria (self): GenMab; Honoraria (self): Gritstone Oncology; Honoraria (self), Speaker Bureau / Expert testimony: Guardant Health; Honoraria (self), Advisory / Consultancy: Lilly; Honoraria (self), Advisory / Consultancy: Merck; Honoraria (self): NantOmics; Honoraria (self): OncoPlex Diagnostics; Honoraria (self), Advisory / Consultancy: Taiho Pharmaceutical; Advisory / Consultancy: Astellas Pharma. H. Park: Research grant / Funding (institution): Amgen; Research grant / Funding (institution): AstraZeneca; Research grant / Funding (institution): Bayer; Research grant / Funding (institution): BeiGene; Research grant / Funding (institution): Bristol-Myers Squibb; Research grant / Funding (institution): Daiichi Sankyo; Research grant / Funding (institution): EMD Serono; Research grant / Funding (institution): Gilead Sciences; Research grant / Funding (institution): Incyte; Research grant / Funding (institution): Lilly; Research grant / Funding (institution): MacroGenics; Research grant / Funding (institution): MedImmune; Research grant / Funding (institution): Medivation; Research grant / Funding (institution): Merck; Research grant / Funding (institution): Millennium; Research grant / Funding (institution): Novartis; Research grant / Funding (institution): Pfizer; Research grant / Funding (institution): Puma Biotechnology; Research grant / Funding (institution): Regeneron; Research grant / Funding (institution): Roche; Research grant / Funding (institution): Taiho Pharmaceutical; Research grant / Funding (institution): Vertex. H. Uronis: Shareholder / Stockholder / Stock options, Full / Part-time employment: GeneCentric; Advisory / Consultancy, Research grant / Funding (institution), Travel / Accommodation / Expenses: Bristol-Myers Squibb; Research grant / Funding (institution): Advaxis; Research grant / Funding (institution): Genentech/Roche; Research grant / Funding (institution): Lycera; Research grant / Funding (institution): MacroGenics; Research grant / Funding (institution): Merck. Y. Kang: Advisory / Consultancy: Bristol-Myers Squibb; Advisory / Consultancy, Research grant / Funding (self): DAE HWA Pharmaceutical; Advisory / Consultancy: Lilly/ImClone; Advisory / Consultancy: Merck/Serono; Advisory / Consultancy: Ono Pharmaceutical; Advisory / Consultancy: Roche/Genentech; Advisory / Consultancy: Taiho Pharmaceutical; Research grant / Funding (self): LSK Biopharma. M.C.H. Ng: Honoraria (self), Advisory / Consultancy, Travel / Accommodation / Expenses: MSD Oncology; Honoraria (self), Travel / Accommodation / Expenses: Taiho Pharmaceutical; Advisory / Consultancy: Bristol-Myers Squibb; Research grant / Funding (institution): ASLAN Pharmaceuticals. P. Enzinger: Advisory / Consultancy: Astellas Pharma; Advisory / Consultancy: Five Prime Therapeutics; Advisory / Consultancy: Merck; Advisory / Consultancy: Taiho Pharmaceutical. K.W. Lee: Research grant / Funding (institution): Array BioPharma; Research grant / Funding (institution): ASLAN Pharmaceuticals; Research grant / Funding (institution): AstraZeneca/MedImmune; Research grant / Funding (institution): Five Prime Therapeutics; Research grant / Funding (institution): Green Cross Corp; Research grant / Funding (institution): LSK BioPharma; Research grant / Funding (institution): MacroGenics; Research grant / Funding (institution): Merck KGaA; Research grant / Funding (institution): MSD; Research grant / Funding (institution): Ono Pharmaceutical; Research grant / Funding (institution): Pfizer; Research grant / Funding (institution): Pharmacyclics; Honoraria (self): Bristol-Myers Squibb; Honoraria (self): Lilly; Research grant / Funding (institution): ALX Oncology. K.H. Lim: Research grant / Funding (institution): Amgen; Research grant / Funding (institution): AstraZeneca; Research grant / Funding (institution): Bayer; Research grant / Funding (institution): BeiGene; Research grant / Funding (institution): Bristol-Myers Squibb; Research grant / Funding (institution): Daiichi Sankyo; Research grant / Funding (institution): EMD Serono; Research grant / Funding (institution): Gilead Sciences; Research grant / Funding (institution): Incyte; Research grant / Funding (institution): Lilly; Research grant / Funding (institution): MacroGenics; Research grant / Funding (institution): MedImmune; Research grant / Funding (institution): Medivation; Research grant / Funding (institution): Merck; Research grant / Funding (institution): Millennium; Research grant / Funding (institution): Novartis; Research grant / Funding (institution): Pfizer; Research grant / Funding (institution): Puma Biotechnology; Research grant / Funding (institution): Regeneron; Research grant / Funding (institution): Roche; Research grant / Funding (institution): Taiho Pharmaceutical; Research grant / Funding (institution): Vertex. J. Lacy: Advisory / Consultancy: AstraZeneca; Advisory / Consultancy: Celgene; Advisory / Consultancy: KeyQuest Health; Advisory / Consultancy: Navigant Consulting; Advisory / Consultancy: Sirtex Medical; Travel / Accommodation / Expenses: Lilly. S.H. Park: Advisory / Consultancy: Lilly. K. Huber: Full / Part-time employment: MacroGenics, Inc. A. Wynter-Horton: Shareholder / Stockholder / Stock options, Full / Part-time employment: MacroGenics, Inc. J. Nordstrom: Shareholder / Stockholder / Stock options, Full / Part-time employment: MacroGenics, Inc. T. Wu: Shareholder / Stockholder / Stock options, Full / Part-time employment: MacroGenics, Inc. J. Wigginton: Leadership role, Shareholder / Stockholder / Stock options, Full / Part-time employment: MacroGenics, Inc. J. Baughman: Shareholder / Stockholder / Stock options, Full / Part-time employment: MacroGenics, Inc. M. Rosales: Shareholder / Stockholder / Stock options, Full / Part-time employment: MacroGenics, Inc. J. Davidson-Moncada: Shareholder / Stockholder / Stock options, Full / Part-time employment: MacroGenics, Inc. Y. Bang: Advisory / Consultancy, Research grant / Funding (institution): AstraZeneca/MedImmune; Advisory / Consultancy, Research grant / Funding (institution): Bayer; Advisory / Consultancy, Research grant / Funding (institution): Beigene; Advisory / Consultancy, Research grant / Funding (institution): Green Cross; Advisory / Consultancy: Hanmi; Advisory / Consultancy, Research grant / Funding (institution): Merck Serono; Advisory / Consultancy, Research grant / Funding (institution): MSD Oncology; Advisory / Consultancy, Research grant / Funding (institution): Novartis; Advisory / Consultancy: Samyang; Advisory / Consultancy, Research grant / Funding (institution): Taiho Pharmaceutical; Research grant / Funding (institution): Astellas Pharma; Research grant / Funding (institution): AstraZeneca/MedImmune; Research grant / Funding (institution): Boehringer Ingelheim; Research grant / Funding (institution): Boston Biomedical; Research grant / Funding (institution): Bristol-Myers Squibb; Research grant / Funding (institution): Genentech/Roche; Research grant / Funding (institution): GlaxoSmithKline; Research grant / Funding (institution): Lilly; Research grant / Funding (institution): MacroGenics; Research grant / Funding (institution): Merck Serono; Research grant / Funding (institution): Ono Pharmaceutical; Research grant / Funding (institution): Pfizer; Research grant / Funding (institution): Takeda. All other authors have declared no conflicts of interest.