Recently, we reported that Prss14/ST14 is an excellent prognostic marker for estrogen receptor negative (ER−) or triple negative (TN) breast cancer type after systemically analyzing the signature genes of breast cancer types (ER, PR, HER2) and the epidermal-mesenchymal transition (EMT) genes using public gene expression data bases [8]. This evidence concerns the gene ESR1 and breast cancer.