KEYNOTE-A17: First-Line Pembrolizumab Plus Cisplatin-Pemetrexed in Japanese Participants With Advanced Pleural Mesothelioma.

Pleural mesothelioma (PM) is an inflammatory cancer linked with asbestos exposure and has a poor prognosis. We report results of the phase 1b KEYNOTE-A17 study (NCT04153565) of first-line pembrolizumab plus chemotherapy in Japanese participants with advanced PM. Participants aged ≥ 20 years with previously untreated, histologically confirmed advanced or unresectable PM received pembrolizumab 200 mg every 3 weeks (Q3W) for ≤ 35 cycles with cisplatin 75 mg/m2 and pemetrexed 500 mg/m2 Q3W for 4-6 cycles. Primary endpoints were the rate of dose-limiting toxicities (DLTs), adverse events (AEs), and treatment discontinuations due to AEs. DLTs were assessed during cycle 1 in 18 participants, and having ≤ 8 participants with DLTs was considered tolerable. AEs were graded per NCI CTCAE 5.0. Tumor response was evaluated per modified RECIST for PM by the investigator. Among 19 participants enrolled, the median study follow-up was 30.8 (range, 27.8-33.3) months (data cutoff September 21, 2022). Of 18 participants evaluated for DLTs, 2 (11%) experienced 4 DLTs (hypoalbuminemia, malaise, pyrexia in 1 participant; uveitis in 1 participant). 18/19 participants (95%) experienced treatment-related AEs; 14 (74%) had grade 3-4 events (no grade 5). Treatment-related AEs led to discontinuation of any drug in 5 participants (26%). The objective response rate was 74% (partial response, n = 14), and the median (range) duration of response was 16.8 (3.0-26.3+) months. First-line pembrolizumab plus chemotherapy was tolerable based on the low incidence of DLTs and showed acceptable safety and preliminary antitumor activity in Japanese participants with advanced PM. Trial Registration: NCT04153565.