It is classified into three subtypes based on the molecular typing, namely, (1) luminal—estrogen receptor (ER) or progesterone receptor (PR) positive or both; (2) human epidermal growth factor receptor 2 (HER2) positive; and (3) triple-negative breast cancer (TNBC), which lack hormone receptor and HER2 expression [2–4]. Here, ESR1 is linked to triple-negative breast carcinoma.