Several potent, selective small-molecule inhibitors targeting CDK4/6 (CDK4/6is) have undergone clinical trials, including palbociclib (PD0332991), abemaciclib (LY-2835219) and ribociclib (LEE001) [6, 7], and gained regulatory approval in combination with hormonal therapy in breast cancer [8–11]. The gene discussed is CDK4; the disease is breast carcinoma.