Real-World Analysis of Adherence to Abemaciclib and Endocrine Therapy in Women With HR+/HER2- Breast Cancer

Background: Adherence to oral anticancer therapies among breast cancer patients is an often-overlooked issue. Lack of patients’ compliance can be caused by several factors, and may hinder the efficacy of prescribed medication, determining shorter than expected survival. In this context, few data are available about adherence to CDK4/6 inhibitors in the real-world practice. We report here the results of a retrospective analysis of adherence to abemaciclib plus endocrine therapy in cohort of women with hormone receptor-positive (HR+), epidermal growth factor 2 negative (HER2-) breast cancer. Methods: Abemaciclib adherence was computed as the ratio between the total number of cycles/months of supply for medication and months between the first and the last prescription. The proportion of Days Covered (PDC) may range from 0 to 1. A score of 0.8 (i.e. 80% adherence rate) was the cutoff to classify the patients as adherent (0.8 ≤ PDC ≤1) or non-adherent (0 ≤ PDC <0.8). Received dose intensity was also calculated. Results: Abemaciclib pharmacy claims of 100 women with HR+/HER2- breast cancer were retrieved. Most patients (91%) were treated in the advanced setting. Abemaciclib were more frequently taken with an aromatase inhibitor (63%), than with fulvestrant (27%). In this population, adherence rate was high (92.25% + 1.939 SD). The proportion of non-adherent patients taking abemaciclib with PDC <0.8 was 12%. There was a significative correlation between the occurrence of side effects and polypharmacy, probably reflecting concomitant non-oncological diseases. Conclusions: Adherence to abemaciclib-based therapy is high in a real-life setting, pending adequate and proactive management of patients. Careful patients’ evaluation and detailed information about expected adverse events are essential to ensure adherence to this antineoplastic agent.