ESR1 and breast cancer: According to the difference in the expression level of different hormone receptors: ERα (estrogen receptor α), PR (progesterone receptor), and HER2 (human epidermal growth factor receptor 2), BC can be briefly classified into four types: luminal A, luminal B, HER2‐positive, and triple‐negative, and of course, the prognosis of each varies [122, 211].