CDK4 and breast cancer: The FDA and EMA have approved abemaciclib and ribociclib, cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, in combination with endocrine therapy (ET) as adjuvant treatment to patients with hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative early breast cancer (EBC) to reduce the risk of recurrence in addition to its use in the treatment of metastatic disease.