Real-world event-free survival with neoadjuvant pembrolizumab plus chemotherapy and adjuvant pembrolizumab in early-stage triple-negative and estrogen receptor-low, HER2-negative breast cancer

Neoadjuvant pembrolizumab plus chemotherapy and adjuvant pembrolizumab has become a standard treatment for patients with early-stage triple-negative breast cancer (TNBC) based on the KEYNOTE-522 trial; however, real-world data on event-free survival (EFS) remain limited. We aimed to evaluate EFS of this regimen and explore the association between immune-related adverse events (irAEs) and EFS. We retrospectively reviewed patients with early-stage TNBC or estrogen receptor-low, HER2-negative breast cancer receiving neoadjuvant pembrolizumab plus chemotherapy at our institution between October 2022 and September 2024. EFS was defined as the time from initiation of neoadjuvant therapy to disease progression, local or distant recurrence, second primary cancer, or death from any cause. EFS was estimated using the Kaplan–Meier method, with log-rank test comparisons. A total of 95 patients were included, with a median age of 52 years. Median follow-up was 24.2 months. Overall pathological complete response (pCR) rate was 62.1%. The estimated 12- and 24-month EFS rates were 96.8% and 88.0% in the overall population, 100.0% and 97.3% in the pCR cohort, and 91.7% and 75.3% in the non-pCR cohort, respectively. EFS was significantly longer in the pCR cohort than in the non-pCR cohort, and all EFS events in the non-pCR cohort occurred within 21 months. Grade 3/4 irAEs occurred in 14 patients, among whom no EFS events were observed during follow-up. This study demonstrated EFS outcomes broadly comparable with those reported in the KEYNOTE-522 trial. The absence of EFS events among patients with severe irAEs was a descriptive, hypothesis-generating observation that warrants further investigation.