Breast cancer is the most commonly diagnosed malignancy in women, and breast cancer is divided into luminal, human epidermal receptor 2 (HER2)-enriched, and triple-negative breast cancer (TNBC) subtypes, according to the presence of distinct molecular markers, including the estrogen receptor (ER), progesterone receptor (PR), and HER2. This evidence concerns the gene ESR1 and triple-negative breast carcinoma.