The Triple Negative Paradox: Primary Tumor Chemosensitivity of Breast Cancer Subtypes

Purpose: Gene expression analysis identifies several breast cancer subtypes. We examined the relationship of neoadjuvant chemotherapy response to outcome among these breast cancer subtypes. Experimental Design: We used immunohistochemical profiles [human epidermal growth factor receptor 2–positive (HER2+)/hormone receptor–negative for HER2+/estrogen receptor–negative (ER−), hormone receptor and HER2− for basal-like, hormone receptor–positive for luminal] to subtype a prospectively maintained data set of patients with breast cancer treated with neoadjuvant anthracycline-based (doxorubicin plus cyclophosphamide, AC) chemotherapy. We analyzed each subtype for clinical and pathologic response to neoadjuvant chemotherapy and examined the relationship of response to distant disease–free survival and overall survival. Results: Of the 107 patients tested, 34 (32%) were basal-like, 11 (10%) were HER2+/ER−, and 62 (58%) were luminal. After neoadjuvant AC, 75% received subsequent chemotherapy and all received endocrine therapy if hormone receptor–positive. The chemotherapy regimen and pretreatment stage did not differ by subtype. Clinical response to AC was higher among the HER2+/ER− (70%) and basal-like (85%) than the luminal subtypes (47%; P < 0.0001). Pathologic complete response occurred in 36% of HER2+/ER−, 27% of basal-like, and 7% of luminal subtypes ( P = 0.01). Despite initial chemosensitivity, patients with the basal-like and HER2+/ER− subtypes had worse distant disease–free survival ( P = 0.04) and overall survival ( P = 0.02) than those with the luminal subtypes. Regardless of subtype, only 2 of 17 patients with pathologic complete response relapsed. The worse outcome among basal-like and HER+/ER− subtypes was due to higher relapse among those with residual disease ( P = 0.003). Conclusions: Basal-like and HER2+/ER− subtypes are more sensitive to anthracycline-based neoadjuvant chemotherapy than luminal breast cancers. Patients that had pathologic complete response to chemotherapy had a good prognosis regardless of subtype. The poorer prognosis of basal-like and HER2+/ER− breast cancers could be explained by a higher likelihood of relapse in those patients in whom pathologic complete response was not achieved.