ERBB2 and breast neoplasm: Breast tumors can be classified into 5 intrinsic subtypes based on differences in patterns of gene expression: (1) basal-like; (2) human epithelial receptor-2-positive (HER2)/neu, also known as ErbB2+; (3) luminal-like A; (4) luminal-like B; and (5) the normal breast tissue-like subtype [4].