By gene expression profiling and IHC markers, breast cancers can be classified into five major subtypes: luminal A (ER + and/or PR+, HER2-), luminal B (ER + and/or PR+, HER2+), HER2-overexpressing (ER-, PR-, HER2+), basal-like (ER-, PR-, HER2-, CK5/6+ and/or EGFR+) and normal breast-like tumors[1,8,12,24,25]. This evidence concerns the gene ESR1 and breast cancer.