Impacts and predictors of cytotoxic anticancer agents in different breast cancer subtypes

Breast cancer is not a single entity. This study therefore aimed to identify differences in the impacts of anticancer agents and predictive factors between different breast cancer subtypes. A total of 234 patients with luminal (n = 109), luminal-HER2 (L-H, n = 29), HER-2 (n = 35), or triple negative (TN, n = 61) breast cancer subtypes were treated with standard neoadjuvant chemotherapy consisting of an anthracycline and/or taxane. Pathological response and prognosis were examined in each subtype. Expression levels of estrogen and progesterone receptors, HER-2, nuclear grade, MIB-1, p53, topoisomerase IIalpha (topoIIalpha), cytokeratin (CK) 5/6, and epidermal growth factor receptor (EGFR) were examined in association with quasipathological complete response (QpCR). QpCR rates were 9.1% (10/109) in luminal, 45% (13/29) in L-H, 37% (13/35) in HER2, and 54.1% (33/61) in TN. Non-QpCR patients showed significantly poorer 3-year disease-free survival than QpCR patients in TN, but not in patients with other subtypes. No factors were associated with QpCR in luminal patients. Patients with higher nuclear grade were more likely to achieve QpCR in L-H. The proliferative markers MIB-1 and topoIlalpha had opposite impacts on pathological response in HER-2 and TN. The QpCR rate was significantly higher in TN lacking CK5/6 and/or EGFR expression, defined as nonbasal subtype, compared with basal subtype (p = 0.049). Cytotoxic anticancer agents were associated with different responses in different breast cancer subtypes. Identifying basal-type cancer and further subdivision of nonbasal types is important for treating TN patients.