Efficacy of Pembrolizumab Monotherapy in Japanese Patients with Advanced Gastric or Gastroesophageal Junction Cancer

Purpose Pembrolizumab demonstrated antitumor activity in programmed death ligand 1 positive (combined positive score (CPS) ≥ 1) gastric/gastroesophageal junction cancer in KEYNOTE-059 (third line or beyond), KEYNOTE-061 (second line), and KEYNOTE-062 (first line). We characterized efficacy and safety of pembrolizumab monotherapy in Japanese patients across several lines of therapy in these studies. Methods This analysis was conducted in 34 patients from KEYNOTE-059 cohort 1 (all pembrolizumab), including 13 patients with CPS ≥ 1, 65 patients with CPS ≥ 1 from KEYNOTE-061 (pembrolizumab, n = 27; chemotherapy, n = 38), and 70 patients with CPS ≥ 1 from KEYNOTE-062 (pembrolizumab, n = 38; chemotherapy, n = 32). Overall survival (OS), progression-free survival (PFS), objective response rate (ORR), and safety were evaluated. Results In KEYNOTE-059, ORR with pembrolizumab was 9%, median PFS was 2 months, and median OS was 10 months. In KEYNOTE-061, median OS was 12 months with pembrolizumab versus 10 months with chemotherapy (hazard ratio (HR), 0.67; 95% confidence interval (CI), 0.39–1.15). Median PFS (pembrolizumab vs. chemotherapy) was 2 months versus 4 months (HR, 1.21; 95% CI, 0.69–2.13); ORR was 7% versus 18%. In KEYNOTE-062, median OS was 20 months with pembrolizumab versus 18 months with chemotherapy (HR, 0.76; 95% CI, 0.43–1.33). Median PFS (pembrolizumab vs. chemotherapy) was 6 months versus 7 months (HR, 1.03; 95% CI, 0.61–1.74); ORR was 29% versus 34%. Conclusions The current analysis provides valuable information that anti–PD-1 therapies are worthy of further assessment for gastric cancer. Trial Registration ClinicalTrials.gov: NCT02335411 (KEYNOTE-059), NCT02370498 (KEYNOTE-061), and NCT02494583 (KEYNOTE-062).