Effectiveness and safety of pembrolizumab for the treatment of Japanese patients with microsatellite instability-high tumors excluding colorectal cancer: a post-marketing surveillance.

Background: We aimed to assess the real-world effectiveness and safety of pembrolizumab monotherapy in Japanese patients with high-frequency microsatellite instability (MSI-H) solid tumors except colorectal cancer.

Methods: This multicenter, observational, post-marketing surveillance had a 12-month observation period. We included all patients with locally advanced or metastatic MSI-H solid tumors, except colorectal cancer, in whom standard treatment was difficult or who had shown tumor progression after conventional chemotherapies and had started treatment with pembrolizumab by 31 December 2019.

Results: In total, 403 patients were enrolled, and 396 and 376 patients were included in the safety and effectiveness analysis sets, respectively. The numbers of patients and frequencies of tumor types occurring in ≥20 cases were: endometrial, 162/403 (40.2%); gastric, 61/403 (15.1%); biliary tract, 42/403 (10.4%); pancreatic, 29/403 (7.2%); and ovarian, 20/403 (5.0%). The objective response rate was 50.3% (189/376) and the disease control rate was 71.5% (269/376). The 12-month progression-free survival (PFS) rate was 42.1% and the median PFS was 8.8 months (95% confidence interval, 6.4-11.5). The 12-month overall survival (OS) rate was 75.1%, and median OS was not reached. Treatment-related adverse events (AEs) of special interest of any grade occurred in 128/396 (32.3%) patients, and those of Grade ≥ 3, in 54/396 (13.6%) patients. One patient with esophageal cancer experienced a Grade 5 AE. No new safety signals were observed.

Conclusions: This study confirmed the real-world effectiveness and safety of pembrolizumab monotherapy in patients with MSI-H solid tumors except colorectal cancer in Japan.