Review of cyclin-dependent kinase 4/6 inhibitors in the treatment of advanced or metastatic breast cancer.

Objective: The purpose of this study is to review CDK 4/6 inhibitors used to treat metastatic breast cancer for patient safety, cost and utilization. By evaluating patient outcomes and payer influence, this study will provide critical information to aid prescribers in therapeutic decisions.

Methods: This retrospective cohort study included patients from a national specialty pharmacy with a diagnosis of breast cancer and received either palbociclib, abemaciclib, or ribociclib for treatment. Patients were stratified into four subgroups based on their total oncolytic regimen at the time of their first eligible study medication dispense. Pharmacy claims data were reviewed to determine cost and therapy adherence.

Results: The mean proportion of days covered was highest in patients on combination therapy with a hormone agent, 81.0%. While secondary insurances largely affected final patient out-of-pocket costs, final copays were significantly lower than the average wholesale price (AWP) of each CDK 4/6 inhibitor. When analyzing patient reported side effects, over 60% of the study population did not experience an adverse drug event (ADE) during the study time period. Ribociclib had the fewest number of reported side effects with abemaciclib patients reporting the most. Although reported ADE profiles were similar across all three study medications, difference in frequency should be evaluated when considering medication choice with specific comorbidities.

Conclusion: CDK 4/6 inhibitors have demonstrated safety and tolerability in HR-positive/HER2-negative breast cancer patients. Real world safety data and out-of-pocket patient costs in addition patient specific comorbidities should be considered when developing a treatment plan that includes a CDK 4/6 inhibitor selection.