ESR1 and breast carcinoma: Gallen International Breast Cancer Conference released a new definition of breast cancer molecular subtypes: luminal A (ER/PR+, HER2−, Ki67+ < 20%, with the percentage indicating the IHC staining results for patient samples), luminal B (ER/PR+ < 20%, HER2−, Ki67+ ≥ 20%); HER2+ B2 (ER/PR+, HER2 overexpression), HER2 overexpression (ER−, PR−, HER2 overexpression), basal-like triple-negative breast cancer (TNBC, ER−, PR−, and HER2−), and other special subtypes (10).