There are three types of breast cancer based on molecular and histological findings: breast cancer expressing hormone receptors (estrogen receptor positive (ER+) or progesterone receptor positive (PR+)), breast cancer expressing human epidermal growth factor receptor 2 (HER2+), and triple-negative breast cancer (TNBC) (ER-, PR-, HER2-) [17,18]. Here, ESR1 is linked to breast cancer.