Clinically, breast cancer comprises three main subtypes including human epidermal growth factor receptor 2 (HER2) positive, hormone receptor [estrogen receptor (ER) and/or progesterone receptor (PGR)]-positive, and triple-negative breast cancer (TNBC) which lacks expression of ER, PGR, and HER2 7, 8. Here, ESR1 is linked to triple-negative breast carcinoma.