BACKGROUND: Neoadjuvant pembrolizumab plus chemotherapy and adjuvant pembrolizumab have been established as the optimal systemic therapies for patients with early stage triple-negative breast cancer (TNBC)
however, their efficacy and feasibility in the Japanese population remain unexplored. METHODS: This study included patients with early stage TNBC or low estrogen receptor (ER) positivity (1-9%) with human epidermal growth factor receptor type 2- (HER2-) negative breast cancer who received neoadjuvant pembrolizumab plus chemotherapy from October 2022 at Cancer Institute Hospital of Japanese Foundation for Cancer Research. Information regarding clinicopathological features, systemic therapy, treatment outcomes, and adverse events of patients who underwent surgery by February 2024 was retrospectively collected. RESULTS: Overall, 69 patients received neoadjuvant pembrolizumab plus carboplatin and paclitaxel therapy, and 46 underwent surgery by February 2024. The median age of the patients was 53.5 years, and 80.4% and 19.6% had stage II and III disease, respectively. TNBC and ER-low HER2-negative breast cancer accounted for 82.6% and 17.4% cases, respectively. Overall pathological complete response rate was 56.5%, with 87.5% in patients with ER-low HER2-negative tumors. The completion rates for neoadjuvant pembrolizumab, chemotherapy, and pembrolizumab plus chemotherapy were 65.2%, 56.5%, and 52.2%, respectively. Furthermore, 80.4% and 15.2% of patients experienced grade 3 or higher treatment-related adverse events and immune-related adverse events, respectively, and 34% experienced unexpected hospitalization during neoadjuvant treatment. CONCLUSIONS: The efficacy and safety profiles of neoadjuvant pembrolizumab plus chemotherapy in the Japanese population are consistent with previous reports. This regimen may have therapeutic potential against ER-low HER2-negative tumors and TNBC.