ESR1 and cancer: Deregulated functions of NCoR and SMRT have been observed in various cancers, including breast and prostate cancer.[48, 49, 50] For instance, the levels of NCoR/SMRT, co‐repressors of the transcription factor estrogen receptor α (ERα), are critical for the repression of ERα transcriptional activity and ERα target gene transcription mediated by tamoxifen, a well‐known drug used for breast cancer therapy.