CDK4 and neoplasm: Several studies have suggested that the CDK4/6 inhibitors bind to the ATP-binding pocket of CDK4 and CDK6 (Mariaule and Belmont, 2014) and block the cell proliferation in a wide range of tumors and reduce tumor growth in cancer xenograft models (Fry et al., 2004; Marzec et al., 2006; Logan et al., 2013; Tate et al., 2014; Gong et al., 2017; Kim et al., 2018).