ESR1 and breast cancer: Currently recognized cytokines that evaluate the therapeutic effect and prognosis of breast cancer include estrogen receptor (ER), progesterone (PR), human epidermal growth factor receptor (2), human epidermal growth factor receptor-2 (HER-2), and nucleus-associated antigen Ki-67, which play a synergistic role in the development of breast cancer via influencing the occurrence, development, and prognosis of breast cancer [3, 4].