BC is a very heterogeneous disease and is categorized into five molecular subtypes: HER2+, basal (ER−/HER2−/PR−), luminal A (ER+/HER2, with a low-proliferative phenotype), luminal B (ER+/HER2, with a high-proliferative phenotype), and normal BC [17]. The gene discussed is ERBB2; the disease is breast cancer.