Immunohistochemical surrogate markers of breast cancer molecular classes predicts response to neoadjuvant chemotherapy

Abstract

Complete pathologic response to neoadjuvant chemotherapy (NACT) is predominantly seen in "ERBB2" and "basal-like" tumors using expression profiling. We hypothesize that a similar response could be predicted using semiquantitative immunohistochemistry for estrogen receptors (ER), progesterone receptors (PR), and human epidermal growth factor receptor 2 (HER2). ER, PR, and HER2 were used to classify 359 tumors treated with NACT into 6 groups: luminal A (strong ER+, HER2 negative), luminal B (weak to moderate ER+, HER2 negative), triple negative (negative for ER, PR, and HER2), ERBB2 (negative for ER and PR, but HER2+), luminal A-HER2 hybrid (strong ER+ and HER2+), and luminal B-HER2 hybrid (weak to moderate ER+ and HER2+). Complete pathologic response was defined as absence of invasive carcinoma in the breast and regional lymph nodes. Thirteen percent (48 of 359) demonstrated complete pathologic response. The highest rate of complete pathologic response was seen in ERBB2 (33%; 19 of 57) and triple negative (30%; 24 of 79) tumor classes. Among the ER+ "molecular" group, the highest rate of complete pathologic response was seen among luminal B-HER2 hybrid tumors, 8% (2 of 24). Remainder of ER+ tumors demonstrated a very low rate of complete pathologic response, 1.5% (3 of 198). The 5-year survival for patients achieving complete pathologic response was 96% compared with 75% in patients that failed to achieve complete pathologic response. The overall survival was worse in the ER-negative group (ERBB2 and triple negative) compared with the ER-positive group. We confirm the recently defined "triple negative paradox," or rather "hormone receptor negative paradox," that despite the best response to NACT, ERBB2 and triple negative tumors show the worst overall survival because of higher relapse among those with residual disease.