Molecular determinants of clinical outcomes with pembrolizumab versus paclitaxel in a randomized, open-label, phase III trial in patients with gastroesophageal adenocarcinoma.

Background: In the phase III KEYNOTE-061 trial (NCT02370498), pembrolizumab did not significantly improve overall survival versus paclitaxel as second-line therapy for gastric/gastroesophageal junction (GEJ) adenocarcinoma with programmed death-ligand 1 (PD-L1) combined positive score (CPS) ≥1 tumors. The association of tissue tumor mutational burden (tTMB) status and clinical outcomes was determined, including the relationship with CPS and microsatellite instability-high (MSI-H) status.
Patients and Methods: In patients with whole exome sequencing (WES) data [420/592 (71%); pembrolizumab, 218; paclitaxel, 202], the association of tTMB with objective response rate (ORR; logistic regression), progression-free survival (PFS; Cox proportional hazards regression), and overall survival (OS; Cox proportional hazards regression) were measured using one-sided (pembrolizumab) and two-sided [paclitaxel] P values. tTMB was also evaluated using FoundationOne®CDx [205/592 (35%)]. Prespecified equivalent cut-offs of 175 mut/exome for WES and 10 mut/Mb for FoundationOne®CDx were used.
Results: WES-tTMB was significantly associated with ORR, PFS, and OS in pembrolizumab-treated (all P < 0.001) but not paclitaxel-treated patients (all P > 0.6) in univariate analysis. The area under the receiver operating characteristics curve for WES-tTMB and response was 0.68 [95% confidence interval (CI) 0.56-0.81] for pembrolizumab and 0.51 (95% CI 0.39-0.63) for paclitaxel in univariate analysis. There was low correlation between WES-tTMB and CPS in both treatment groups (r ≤ 0.16). WES-tTMB remained significantly associated with all clinical endpoints with pembrolizumab after adjusting for CPS and with PFS and OS after excluding known MSI-H tumors (n = 26). FoundationOne®CDx-tTMB demonstrated a positive association with ORR, PFS, and OS in pembrolizumab-treated patients (all P ≤ 0.003) but not PFS or OS in paclitaxel-treated patients (P > 0.1).
Conclusion: This exploratory analysis from KEYNOTE-061 is the first to demonstrate a strong association between tTMB and efficacy with pembrolizumab but not paclitaxel in patients with gastric/GEJ adenocarcinoma in a randomized setting. Data further suggest tTMB is a significant and independent predictor beyond PD-L1 status.
Competing Interests: Disclosure KS reports honoraria for AbbVie, Novartis, and Yakult; consulting or advisory role for AbbVie, Astellas Pharma, Bristol Myers Squibb, Eli Lilly, Glaxo Smith Kline, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Novartis, Ono Pharmaceutical, Pfizer, Taiho, and Takeda; researching funding for Astellas Pharma, Chugai Pharmaceutical, Daiichi Sankyo, Dainippon Sumitomo Pharma, Eli Lilly, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Medi Science, Ono Pharmaceutical, and Taiho Pharmaceutical. MÖ reports honoraria for Astellas Pharma, Janssen, and Roche; consulting or advisory role for Janssen; and travel, accommodations, expenses for AstraZeneca. Y-JB reports consulting/advisory for Astellas, AstraZeneca, Bayer, BeiGene, BMS, Daiichi Sankyo, Eli Lilly, Genentech/Roche, Genexine, Green Cross, Hammi, Merck Serono, MSD, Novartis, Samyang Biopharm, and Taiho; grants (to the institution for clinical trials) from Astellas, AstraZeneca, Bayer, BeiGene, Boehringer Ingelheim, Bostin Biomedical, BMS, CKD Pharma, Curis, Daiichi-Sankyo, Eli Lilly, Five Prime, Genentech/Roche, Genexine Green Cross, GSK, MacroGenics, Merck Serono, MSD, Novartis, Ono, Pfizer, Taiho, and Takeda. MDB reports honoraria for Eli Lilly, Merck Serono, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and Servier; consulting or advisory role for Eli Lilly; speakers’ bureau for Eli Lilly and Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA; researching funding for Eli Lilly; and travel, accommodations, expenses for Roche. MM reports honoraria for Bristol Myers Squibb, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Novartis, and Pierre Fabre; consulting or advisory role for Bristol Myers Squibb, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Novartis, and Pierre Fabre; speakers’ bureau for Bristol Myers Squibb, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Novartis, and Pierre Fabre; and research funding for Novartis and Roche. M-HR reports honoraria for Bristol Myers Squibb, Daehwa Pharmaceutical, Eli Lilly, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Novartis, Ono Pharmaceutical, and Taiho; and consulting or advisory role for Bristol Myers Squibb, Daehwa Pharmaceutical, Eli Lilly, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Novartis, Ono Pharmaceutical, and Taiho. CC reports honoraria for Andes Biotechnologies; consulting or advisory role for Boehringer Ingelheim Bristol Myers Squibb, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and Roche; speakers’ bureau for Bristol Myers Squibb, Eli Lilly, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and Roche; research funding for AstraZeneca, Astella Pharma, Bristol Myers Squibb, Medivation, and Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA; and travel, accommodations, expenses for Bristol Myers Squibb and Roche. HCC reports honoraria for Eli Lilly and Merck Serono; consulting or advisory role for Amgen, BeiGene, Bristol Myers Squibb, Celltrion, Eli Lilly, Gloria, Merck Serono, Quintiles, Taiho, and Zymeworks; and research funding for Amgen, BeiGene, Bristol Myers Squibb/Ono Pharmaceutical, Eli Lilly, Glaxo Smith Kline, Merch Serono, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and Taiho. KM reports research funding (to his institution) from Daiichi Sankyo, MEDISCIENCE PLANNING, MSD, Parexel International, Pfizer, Sanofi, Solasia Pharma, and Sumitomo Dainippon Pharma; honoraria for speaking from Bristol Myers Squibb, Chugai Pharmaceutical, Eli Lilly, Ono Pharmaceutical Co., Ltd., Taiho Pharmaceutical, Takeda Pharmaceutical, and Sanofi; and advisory/consultancy for Amgen, AstraZeneca, and Ono Pharmaceutical Co., Ltd. EVC reports consulting or advisory role for Array BioPharma, AstraZeneca, Bayer, Bristol Myers Squibb, Celgene, Eli Lilly, Halozyme, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Merck KGaA, Novartis, Roche, and Servier; and research funding (to his institution) for Amgen, Bayer, Boehringer Ingelheim, Bristol Myers Squibb, Celgene, Eli Lilly, Ipsen, Merck Sharp and Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Merck KGaA, Novartis, Roche, and Servier. JK is an employee of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and stockholder of Merck & Co., Inc., Kenilworth, NJ, USA. RC is an employee of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and stockholder of Merck & Co., Inc., Kenilworth, NJ, USA. DA-G is an employee of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA and stockholder of Merck & Co., Inc., Kenilworth, NJ, USA and received travel, accommodations, or expenses from Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA. JL is an employee of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA. C-SS is an employee of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc, and received researching funding and travel, accommodations, or expenses for Exelixis. DA is an employee of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and stockholder of Merck & Co., Inc., Kenilworth, NJ, USA. ZAC is an employee of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, and has stock ownership interests in Merck & Co., Inc., Kenilworth, NJ, USA, and in Bristol Myers Squibb. CSF served in an advisory/consultancy role for Agios, Amylin Pharmaceuticals, AstraZeneca, Bain Capital, CytomX Therapeutics, Daiichi Sankyo, Eli Lilly, Entrinsic Health, EvolveImmune Therapeutics, Genentech, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Taiho, and Unum Therapeutics. He also serves as a director for CytomX Therapeutics and owns unexercised stock options for CytomX and Entrinsic Health; is a cofounder of EvolveImmune Therapeutics and has equity in this private company; and has provided expert testimony for Amylin Pharmaceuticals and Eli Lilly.
(Copyright © 2021 European Society for Medical Oncology. Published by Elsevier Ltd. All rights reserved.)