With advances in our knowledge about this disease at molecular level, breast cancer now is unambiguously classified into four subtypes including Luminal A (ER+/PR+/HER2−, grade 1 or grade 2), Luminal B (ER+/PR+/HER2+, grade 3), HER2 overexpression (ER−/PR−/HER2+) and Triple Negative Breast Cancer (TNBC, ER−/PR−/HER2−) [6]. The gene discussed is ERBB2; the disease is breast cancer.