ESR1 and breast cancer: Breast cancer (BC) imposes a huge economic and health burden on women worldwide.[1] Triple‐negative breast cancer (TNBC), which lacks expression of the estrogen receptor (ER), human epidermal growth factor receptor 2 (HER2), and progesterone receptor (PR), is a highly aggressive type of BC, accounting for approximately 15% of all BC cases.[2] Tumor resection in combination with chemotherapy is currently recommended for TNBC treatment.