Factors associated with adjuvant endocrine therapy adherence in non-metastatic breast cancer.

533 Background: Over 50% of breast cancer patients prescribed adjuvant endocrine therapy (ET) are nonadherent during the recommended 5-year course of therapy. We investigated the role of cancer medication delivery on adherence, including mail order pharmacy use, number of pharmacies and copays. Methods: We conducted a retrospective cohort study of 15,769 commercially insured breast cancer patients age 18-64 with newly diagnosed breast cancer in 2007-2015 that initiated ET. Incident breast cancer was identified by a validated algorithm which identifies mainly non-metastatic breast cancer. We examined the association between 12-month AET adherence (proportion of days covered by fills ≥0.80) and mail order pharmacy use, number of pharmacies, and AET copays. We used Poisson regression to estimate nonadherence risk ratios and adjusted for demographics (age, income, race, urbanicity), comorbidities, total medications, primary cancer treatments (surgery, radiation, chemo, and ET initiated), and generic AI availability. Sensitivity analyses were conducted using alternate specifications for independent variables. To test whether any observed differences were due to self-selection, we also conducted a negative control analysis. Results: Most patients were white (74.4%) and age 55-64 (43.3%). Only 16% of patients used a mail order pharmacy for ET fills, most patients only used one pharmacy (58.8%) and 25.2% had a co-pay of $20 or more. In the primary analysis, mail order patients were more likely to be adherent to their ET (aRR 1.21; 95% CI 1.18-1.24), patients using one pharmacy were more likely to be adherent (1 vs 3+: aRR 1.09; 95% CI 1.06-1.13), and patients with lower copays were more likely to be adherent (quartile 1 vs 4: aRR 1.04; 95% CI 1.01-1.08). Results were consistent across sensitivity analyses, and there was no association between mail order and copays and the negative control outcome of any pneumonia diagnoses. Conclusions: Medication delivery factors are associated with adherence to breast cancer AET. Future work should investigate whether interventions to streamline medication delivery could improve adherence for this population.