DISCUSSION
toxicity, TNBC
CPS, DISEASE
In this subset analysis of patients in the phase 3 KEYNOTE‐355 study enrolled in Japan, pembrolizumab plus chemotherapy improved outcomes versus placebo plus chemotherapy in patients with previously untreated locally recurrent inoperable or metastatic TNBC. Baseline characteristics were generally consistent among Japanese patients and those enrolled in the global population.The magnitude of treatment benefit with pembrolizumab plus chemotherapy versus placebo plus chemotherapy appeared greater in Japanese patients than in the global study across each of the PD‐L1 CPS populations (i.e., PD‐L1 CPS ≥10, PD‐L1 CPS ≥1, and the intention‐to‐treat population).The ORRs and disease control rates were generally similar between the treatment groups in the Japan subset and the global study in each of the PD‐L1 CPS populations.The toxicity profile was generally consistent with the profile reported for the global study.In a subgroup analysis of Japanese patients (A limitation of this study is that the Japanese subset comprises a portion of patients enrolled globally in KEYNOTE‐355 (87 of 847 patients) and no alpha was allocated to this analysis. Secondly, given the small number of patients in this analysis, we were not able to perform any meaningful subset analyses, including assessments of clinical benefit with different routinely used chemotherapy regimens, assessment of the influence of differences in clinical characteristics on outcomes, or differences in treatment patterns. In the current study, the allocation of patients to nab‐paclitaxel, paclitaxel, or gemcitabine–carboplatin was by investigator's choice. At the time of writing, there is no unequivocal evidence for whether either of these chemotherapy regimens provides more clinical benefit than the other in this setting.In Japanese patients enrolled in KEYNOTE‐355, pembrolizumab plus chemotherapy tended to show improvements in OS and PFS with manageable toxicity versus placebo plus chemotherapy, consistent with the global population. These findings provide support for the use of pembrolizumab plus chemotherapy in Japanese patients with previously untreated locally recurrent inoperable or metastatic TNBC.