In this review, we mainly overviewed the clinical trials about the beneficial effects of Palbociclib (Table 1), Ribociclib (Table 2) and Abemaciclib (Table 3) in breast cancer with their tolerable adverse effects, and discussed their resistant mechanisms thus looking for useful biomarkers to predict the efficiency of the CDK4/6 inhibitors. Here, CDK4 is linked to breast carcinoma.