ERBB2 and breast cancer: Based on the presence or absence of progesterone receptors, estrogen receptors, and human epidermal growth factor receptor-2 (HER-2), BC can be roughly divided into three different subtypes, namely, intraluminal (luminal A/B) type (positive hormone receptor), HER-2 type (overexpression of HER-2), and triple-negative BC (TNBC) (the loss of all three receptors) (3).