CDK4 and breast cancer: In conclusion, we found that ribociclib effectively inhibited the CDK4/6 signaling pathways in TNBC cell lines (MDA-MB-231 and MDA-MB-468) and BC cell (MCF-7) growth, and the expression of AR might contribute to ribociclib-mediated G1 arrest in AR-positive cell lines (MDA-MB-231 and MCF-7 cell lines).