Clinical significance of basal-like subtype in triple-negative breast cancer

Background No clinically useful target molecule has been identified for triple-negative (TN) breast cancer, i.e., estrogen receptor (ER)-negative, progesterone receptor (PgR)-negative, human epidermal growth factor receptor-2 (HER2)-negative phenotype, and its prognosis is poor. Triple-negative cancer consists of two subtypes: basal-like and non-basal-like. The aim of this study is to clarify the clinical and biological characteristics of these two subtypes of TN cancer. Methods We examined, by immunohistochemistry, expression of biological markers cytokeratin (CK) 5/6 and epidermal growth factor receptor (EGFR) in triple-negative breast cancer. Basal-like subtype was defined as CK5/6-positive and/or EGFR-positive, and non-basal-like subtype was defined as no expression of these two markers. We studied the correlation between basal-like subtype and several factors related to tumor progression, along with the prognostic value of basal-like subtype and other biological markers in triple-negative cancer. Results In the 48 cases of operable triple-negative breast cancer, basal-like subtype was detected in 22 (45.8%) and non-basal-like subtype in 26 (54.2%). Basal-like subtype was significantly correlated with nodal status (P = 0.0475) and nuclear grade (P = 0.0475). Basal-like subtype was also significantly associated with Ki67 labeling index (P = 0.0118), c-kit expression (P = 0.0335), and aurora A expression (P = 0.0020). No association was detected between basal-like cancer and other biological markers. Patients with basal-like subtype of triple-negative cancer showed shorter disease-free survival (P = 0.0049) and overall survival (P = 0.0283) than patients with non-basal-like subtype. No independent prognostic factors were identified among the prognostic factors obtained from univariate analysis. Conclusions These findings suggest that basal markers can be used to classify triple-negative breast cancer into at least two subtypes with differing prognoses. It is necessary to develop a novel treatment strategy to improve the prognosis of patients with basal-like subtype of triple-negative breast cancer.