ESR1 and breast cancer: Currently, it has emerged as the cancer category exhibiting the highest rate of newly diagnosed cases globally, as well as the malignant neoplasm with the highest occurrence rate among women.1 One of the most dangerous subtypes of BC is triple-negative breast cancer (TNBC), which is characterized by the absence of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2).