ERBB2 and breast cancer: Gallen defined the following BC molecular subtypes: luminal A, luminal B, human epidermal growth factor receptor-type 2(HER2)-enriched (HER2E), and triple-negative (TNBC), based on immunohistochemical classification for estrogen, progesterone, and HER2 receptors (the last confirmed by fluorescence in situ hybridization).