ESR1 and breast cancer: This retrospective study assessed the mRNA-based MammaTyper® assay's capability of predicting pCR with NACT, and ER, PR, Ki67, and HER2 status at immunohistochemical (IHC) through transcriptomics.<h4>Methods</h4>Diagnostic biopsies from 76 BC patients treated at the Cremona Hospital between 2012-2018 were analyzed.