Survival outcomes after systemic treatment of high-grade triple-negative metaplastic breast cancer versus triple-negative breast cancer of no special type.

This study aimed to evaluate the prognostic impact of adjuvant and neoadjuvant chemotherapy (ACT, NACT) in high-grade triple-negative metaplastic breast cancer (TNMBC) and to compare survival outcomes with those of triple-negative breast cancer of no special type (TNBC NST). A total of 73 patients with high-grade TNMBC and 369 patients with TNBC NST were included in the study. In the non-NACT and ACT subgroups, TNMBC patients exhibited significantly worse overall survival (OS), distant disease-free survival (DDFS), breast cancer-specific survival (BCSS), and disease-free survival (DFS) than TNBC NST patients (non-NACT: p < 0.001 for all endpoints; ACT: OS, p < 0.001; DDFS, p < 0.001; BCSS, p = 0.004; DFS, p < 0.001). In the NACT subgroup, TNMBC and TNBC NST patients had similar survival outcomes. Within the TNMBC cohort, patients treated with NACT without achieving a pathological complete response (pCR) demonstrated improved OS (p = 0.045) and a trend toward improved BCSS (p = 0.056) compared to TNMBC patients who did not receive CT. No significant survival difference was observed between TNMBC patients treated with ACT and those without CT, nor between NACT-treated TNMBC patients without a pCR and those treated with ACT. We conclude that survival outcomes of TNMBC vs. TNBC NST patients may be influenced by systemic treatment. NACT-treated TNMBC patients without a pCR demonstrated superior OS compared to TNMBC patients receiving no CT, while no survival difference was observed among TNMBC patients based on treatment sequencing (ACT vs. NACT).