According to the expression of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER‐2), and Ki‐67, breast cancer is classified into four molecular subtypes, including Luminal A, Luminal B, HER‐2‐positive, and triple‐negative.2 As reported, Luminal A showed the best survival among the four subtypes, while triple‐negative breast cancer showed the worst.3, 4 Therefore, molecular subtypes are important for individual treatment and have different prognostic values. The gene discussed is ESR1; the disease is breast cancer.