ERBB2 and breast cancer: Intrinsic molecular breast cancer (BC) whose classification is based on the analysis of global gene expression identifies four main molecular subtypes of BC: luminal A, luminal B, HER2, basal-like, and the more recently identified claudin-low tumor subtype [9,10] Most of the basal-like subtypes lack the expression of ER, PR and HER2, so they are frequently identified as TNBC.