KEYNOTE-025: Phase 1b study of pembrolizumab in Japanese patients with previously treated programmed death ligand 1-positive advanced non-small-cell lung cancer.

Pembrolizumab, a humanized monoclonal antibody against programmed death 1 (PD-1), has been shown to improve overall survival (OS) in patients with previously treated advanced non-small-cell lung cancer (NSCLC) with programmed death ligand 1 (PD-L1) tumor proportion score (TPS) ≥1%. We report safety and efficacy results from the phase 1b KEYNOTE-025 study, which evaluated pembrolizumab in Japanese patients with previously treated NSCLC. Eligible patients had histologically/cytologically confirmed advanced NSCLC with PD-L1 TPS ≥1% and had received ≥1 platinum-doublet chemotherapy. Patients received pembrolizumab 10 mg/kg once every 3 weeks for 2 years or until disease progression/unacceptable toxicity. Primary objectives were to evaluate the safety of pembrolizumab in patients with PD-L1 TPS ≥1% and the objective response rate (ORR) per RECIST version 1.1 in patients with PD-L1 TPS ≥50%. Thirty-eight patients were enrolled and received ≥1 pembrolizumab dose. The median (range) age was 66.0 (41-78) years, and 61% had received ≥2 prior systemic therapies. Eleven patients (29%) experienced grade 3-5 treatment-related adverse events (AE); 9 patients (24%) experienced immune-mediated AE and infusion reactions, with pneumonitis (11%; any grade) being most common. Among evaluable patients with PD-L1 TPS ≥50% (n = 11), ORR was 27% (95% CI, 6-61). Among evaluable patients with PD-L1 TPS ≥1% (n = 37), ORR was 22% (95% CI, 10-38). Median (95% CI) progression-free survival and OS were 3.9 (2.0-6.2) months and 19.2 (8.0-26.7) months, respectively. In summary, pembrolizumab was generally well tolerated and showed promising antitumor activity in Japanese patients with previously treated PD-L1-expressing NSCLC. Outcomes were consistent with those from the phase 3 KEYNOTE-010 study. (Trial registration number: ClinicalTrials.gov, NCT02007070.).