ERBB2 and breast cancer: Based on hormone receptors (estrogen (ER) and progesterone (PR)) and expression level of human epidermal growth factor receptor 2 (HER2), BC can be classified as luminal A (ER + and/or PR + , HER2 −), luminal B (ER + and/or PR + , HER2 +), HER 2-overexpression (ER − , PR − , and HER2 +), triple-negative, and basal-like (ER − , PR − , and HER2-),–luminal A being the most common of all the subtypes [7].