Objective: To evaluate the existing literature regarding the use of cyclin-dependent kinase (CDK) 4/6 inhibitors in the treatment of hormone receptor–positive advanced breast cancer (ABC). Data Sources: A search of the medical literature was performed using PubMed (2014 to June 2018). Search terms included cyclin-dependent kinase, CDK, breast cancer, palbociclib, ribociclib, abemaciclib, PD0332991, LEE011, and LY2835219. Clinicaltrials.gov was also searched. Study Selection and Data Extraction: Trials with clinical efficacy outcomes evaluating CDK 4/6 inhibitors in the treatment of advanced hormone-positive breast cancer were considered. Data Synthesis: Palbociclib, abemaciclib, and ribociclib each demonstrated significant benefit when combined with an aromatase inhibitor, the benefit to patients was similar for each, with an improvement of 42% to 51% in median progression-free survival (PFS). In combination with fulvestrant, CDK 4/6 inhibitors used for the treatment of hormone receptor–positive ABC resulted in a 43% to 58% improvement in median PFS versus fulvestrant alone. CDK inhibitors are relatively well tolerated; however, discontinuation as a result of adverse effects was highest with abemaciclib. Relevance to Patient Care and Clinical Practice: This review considers the use of the 3 commercially available CDK 4/6 inhibitors for treatment of hormone receptor–positive breast cancer, including data on each of the 3 agents in newly advanced and treatment refractory disease. Conclusions: The CDK inhibitors should be used in combination with endocrine therapies for the treatment of ABC. Efficacy of the 3 agents is similar. Selection within the class should include consideration of adverse effects and drug interactions.
Clinical Implications of the Progression‐Free Survival Endpoint for Treatment of Hormone Receptor‐Positive Advanced Breast Cancer