In contrast, COPS5 accelerates the degradation of several tumor suppressor proteins, such as p27,[52] p57,[41] and NCoR.[46] For instance, COPS5 confers tamoxifen resistance by proteasomal degradation of NcoR in ERα‐positive breast cancer.[46] These observations indicated that the regulatory role of COPS5 in protein stability is context‐dependent. This evidence concerns the gene NCOR1 and breast carcinoma.