Currently, the treatment options for breast cancer, including mastectomy, chemotherapy, radiotherapy, hormonal therapy, and immunotherapy, are based on molecular profiles, such as estrogen receptor + (ER+), progesterone receptor + (PR+), human epidermal growth factor receptor 2 + (HER 2+), and triple negative, clinicopathologic features, tumor stage, and tumor grade. Here, ESR1 is linked to breast cancer.