Recently, our group showed that the differential expression of 325 genes in breast biopsies in neoadjuvant chemotherapy were able to stratify, surprisingly, the cases with RD at a rate of 83 and 91% in two independent cohorts (519 and 304 cases), comprising different breast tumor subtypes (ER+HER2-, triple negative, HER2+, and ER-HER-PR+). This evidence concerns the gene ESR1 and breast neoplasm.