The application of molecular profiling to patient samples and the resultant evolving molecular classification of breast cancer have identified at least five subtypes, which can be distinguished by characteristic gene expression profiles: two luminal subsets within estrogen receptor (ER)-expressing tumors and three groups within mostly ER- tumors (HER2, normal breast-like, and the basal-like subtypes) [1]. This evidence concerns the gene ESR1 and breast carcinoma.