Phase 1 study of pembrolizumab (MK-3475; anti-PD-1 monoclonal antibody) in Japanese patients with advanced solid tumors

Background This phase I study evaluated the safety and tolerability, pharmacokinetics and pharmacodynamics, immunogenicity, and antitumor activity of pembrolizumab in Japanese patients with advanced solid tumors. Methods Following an initial dose and a 28-day rest (cycle 1), pembrolizumab was administered as an intravenous infusion at escalating doses (2 or 10 mg/kg) every 2 weeks (Q2W) until disease progression or unacceptable toxicity. Adverse events (AEs) were assessed using CTCAE v4.0, and tumor response was assessed using both RECIST v1.1 and immune-related response criteria (irRC). Full pharmacokinetic sampling was performed during cycle 1. Results Three patients received pembrolizumab at 2.0 mg/kg and seven at 10 mg/kg. No dose-limiting toxicities were observed during cycle 1. Eighty percent of patients experienced drug-related AEs (mostly grade 1 or 2); the most common drug-related AEs were nausea, malaise, pyrexia, and aspartate aminotransferase/alanine transaminase (AST/ALT) elevations (n = 2 each). No drug-related grade 4 or 5 AEs occurred. Immune-related AEs comprised grade 3 ALT elevation (n = 1), grade 3 AST elevation (n = 1), grade 1 pneumonitis (n = 1), and grade 1 thyroid-stimulating hormone elevation (n = 1). The safety and pharmacokinetic profiles of Japanese patients were similar to those previously reported for Caucasian patients. A partial tumor response was observed in one patient with non-small-cell lung cancer (NSCLC) and in one patient with melanoma. Conclusions Pembrolizumab at both 2 and 10 mg/kg Q2W was well tolerated in Japanese patients with advanced solid tumors and showed encouraging anti-tumor activity against melanoma and NSCLC.