ERBB2 and breast cancer: Mammary carcinoma is categorized into different subtypes depending on estrogen/progesterone receptor expression, human epidermal growth factor receptor 2 (HER2) expression and proliferation measured by Ki67 expression, specifically into luminal A (ER/PR+, HER2−, Ki67low), luminal B (ER/PR+, HER2−, Ki67high; or ER/PR+, HER2+), HER2 overexpressing (ER/PR−, HER2+), and triple negative (TNBC) (ER/PR−, HER2−) breast cancer [3,4].