On the basis of the expression levels of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER-2) and proliferation index Ki-67, breast cancer was classified as Luminal A, Luminal B, HER-2 overexpression, triple-negative/basal-like and other subtypes. The gene discussed is ESR1; the disease is breast carcinoma.