Based on the gene expression profiling, the BC has been classified into five intrinsic subtypes with distinct prognostic significance: luminal type A, luminal type B, normal-like, HER-2-positive, and basal-like triple-negative BC (TNBC), in which, 75% of invasive BCs are estrogen receptor 1 + (ESR1 + ) or E2-responsive [3, 4], i.e., luminal subtype. The gene discussed is ESR1; the disease is breast cancer.