Gallen International Breast Cancer Conference, BRCA can be classified into the following subtypes: luminal A (ER/PR+, HER2–, Ki67+ < 20%), luminal B (ER/PR+ < 20%, HER2–, Ki67+ ≥ 20%), HER2+B2 (ER/PR+ and HER2 overexpression), HER2 overexpression (ER–, PR–, and HER2 overexpression), basal-like TNBC (ER–, PR–, and HER2–), and other subtypes (Goldhirsch et al., 2013). Here, ESR1 is linked to breast cancer.