(3) proposed that expression of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor-2 (HER-2) and antigen identified by monoclonal antibody Ki-67 were the main factors determining the classification of breast cancer, which would guide the strategies for targeted therapy, endocrine therapy, or chemotherapy (4, 5). The gene discussed is ESR1; the disease is breast carcinoma.