There were four different molecular subtypes of BC: two subgroups with positive expression of estrogen and/or progesterone receptors (ER+/PR+)—luminal A and B, which account for approximately 70% of all breast cancer cases; one subgroup with overexpression/amplification of the HER/2-neu gene and negative expression of hormonal receptors (HER/2 positive subgroup); and triple-negative breast cancer (TNBC), with no expression of steroid hormone receptors and HER2. The gene discussed is ERBB2; the disease is breast cancer.