ERBB2 and breast cancer: According to the presence/absence of estrogen or progesterone receptors (ER, PR), and amplification of human epidermal growth factor receptor 2 (HER-2, encoded by ERBB2), BC is categorized into three main subtypes: ER+PR+/HER2− (70%), HER+ (15–20%), and triple-negative (15%, TNBC) [4].