Four subtypes can be defined based on clinical and histological evidence such as expression of estrogen (ER) and progesterone receptors (PR), human epidermal growth factor receptor 2 positivity (HER2), and the proliferation factor Ki-67: luminal A (ER and/or PR+, HER2−, Ki-67 low); HER2− negative luminal B (HER2−, ER and/or PR+, Ki-67 high); HER2− positive luminal B (HER2+, ER and/or PR+, any Ki-67); HER2 overexpressed (any Ki-67, HER2+, ER and PR−, HER2 overexpressed); triple-negative breast cancer (TNBC) (ER and PR−, HER2−). The gene discussed is ERBB2; the disease is triple-negative breast carcinoma.