ERBB2 and breast cancer: Human epidermal growth factor receptor 1 (EGFR/HER1), human epidermal growth factor receptor 2 (ErbB2/HER2), human epidermal growth factor receptor 3 (ErbB3/HER3), and human epidermal growth factor receptor 4 (ErbB4/HER4) are four members of the HER family, and the expressions of HER1 (30–40%), HER2 (20–30%), and HER3 (20%) are increased in the case of breast cancer instead of HER4 [35].