The Oncotype Dx® recurrence score (RS), generated by a 21 genes reverse-transcriptase-polymerase-chain-reaction (RT-PCR) assay running in formalin fixed-paraffin embedded (FFPE) specimens, has been demonstrated to outperform traditional clinicopathological criteria in identifying ER + /HER2- early BC patients with a very favorable outcome, who can therefore safely spare CHT4. This evidence concerns the gene ESR1 and breast cancer.