The association of tissue tumor mutational burden (tTMB) using the Foundation Medicine genomic platform with efficacy of pembrolizumab versus paclitaxel in patients (pts) with gastric cancer (GC) from KEYNOTE-061.
Kohei Shitara, Mustafa Özgüroğlu, Yung‐Jue Bang, Maria Di Bartolomeo, Mario Mandalà, Min‐Hee Ryu, Caterina Vivaldi, Tomasz Olesiński, Hyun Cheol Chung, Kei Muro, Eric Van Cutsem, Julie Kobie, Răzvan Cristescu, Deepti Aurora-Garg, Lu Jia, Chie‐Schin Shih, David E. Adelberg, Z. Alexander Cao, David Fabrizio, Charles S. Fuchs
Abstract
4537 Background: KEYNOTE-061 (NCT02370498) was a randomized, open-label, phase 3 study of pembrolizumab vs paclitaxel in pts with advanced gastric or gastroesophageal junction (GEJ) adenocarcinoma with tumor progression after first-line therapy (N = 592). In this analysis, we evaluated tTMB using FoundationOne CDx (F1CDx; Foundation Medicine) in pts with gastric or GEJ cancer in KEYNOTE-061. Methods: In pts with evaluable F1CDx tTMB data (n = 204), we analyzed the association of tTMB with confirmed objective response rate (ORR), progression-free survival (PFS), and overall survival (OS) within each treatment arm using one-sided (pembrolizumab) and two-sided (paclitaxel) Wald test nominal P for logistic regression (ORR) and Cox proportional hazards regression (PFS; OS) adjusted for ECOG performance status; significance was prespecified at 0.05. The clinical utility of tTMB was assessed using the prespecified cutoff of 10 mut/Mb for F1CDx. Clinical data cutoff: Oct 26, 2017. Results: tTMB was positively associated with ORR ( P < 0.001; AUROC, 0.68), PFS ( P < 0.001), and OS ( P = 0.003) with pembrolizumab but not paclitaxel (ORR, P = 0.047; AUROC, 0.30; PFS, P = 0.605; OS, P = 0.084). Pt outcomes by tTMB cutoff are reported in the Table; prevalence of TMB ≥10 mut/Mb was 17%. In pts with microsatellite stable disease-only, HRs (95% CI) by treatment arm for OS by F1CDx cutoff were 0.40 (0.14-1.17) for tTMB ≥10 mut/Mb (n = 21) vs 0.97 (0.70-1.34) for tTMB <10 mut/Mb (n = 168). Conclusions: In this exploratory analysis from KEYNOTE-061, tTMB as determined by F1CDx demonstrated a positive association with clinical outcomes with pembrolizumab, but not paclitaxel, in pts with GC; these findings are consistent with those reported with whole exome sequencing. Pembrolizumab demonstrated an OS benefit vs paclitaxel in the subgroup with tTMB ≥10 mut/Mb, which remained when pts with microsatellite instability-high disease were excluded. Clinical trial information: NCT02370498 . [Table: see text]