According to the expression status of the estrogen receptor α (ERα), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), breast cancer is clinically classified into three main subtypes, including luminal (ERα/PR-positive), HER2-positive, and triple-negative breast cancer (TNBC) 2. Here, ESR1 is linked to triple-negative breast carcinoma.