ERBB2 and breast cancer: BC cells (BCCs) constitute a heterogeneous population that can be classified based on the expression of human epidermal growth factor receptor 2 (HER2), progesterone receptor (PR), and estrogen receptor (ER), as ER+/PR+, HER2+; ER+/PR+, HER2−; ER−/PR−, HER2+; and triple negative (TN), which is characterized by the absence of ER, PR, and HER2 [7,8], and presents the worst prognosis and lowest overall survival [9,10].