CDK4 and cancer: To date, a series of clinical or preclinical evidence has demonstrated effects of CDK4/6 inhibitors in multiple cancers and four drugs, palbociclib (by Pfizer), ribociclib (by Novartis), abemaciclib (by Eli Lilly), and trilaciclib (by G1 Therapeutics), have been approved by Food and Drug Administration (FDA) [30,31] (Figure 3).