ERBB2 and breast cancer: The molecular mechanisms involved in BC pathogenesis have been thoroughly studied, leading to BC classification into three major subtypes: Luminal which is positive for estrogen (ER+) and progesterone receptors (PR+), human epidermal growth factor receptor 2 (HER2+), and basal-like tumors, which lacks hormone receptor and HER2 expression, called triple-negative breast cancer (TNBC)2–4.