Gallen International Breast Cancer Conference issued a new definition of breast cancer molecular subtypes: luminal A (ER/PR+, HER2−, Ki67+ < 20%, with the percentage indicating the immunohistochemical 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 TNBC (ER−, PR−, HER2−), and other special subtypes [2]. This evidence concerns the gene ESR1 and breast cancer.