CDK4 and cancer: The CDK4/CDK6 inhibitors palbociclib, ribociclib and abemaciclib are US Food and Drug Administration (FDA)-approved for treatment of hormone receptor-positive, HER2-negative advanced or metastatic breast cancer after disease progression following endocrine therapy, and these drugs are currently being examined for efficacy in additional solid tumor models, including ccRCC and other cancers with HIF-1α deregulation [5].