Abstract
BACKGROUND: Endocrine therapy adherence remains a barrier to optimal estrogen receptor-positive breast cancer outcomes. We theorized that experience navigating difficult medication regimen factors, such as route of administration complexity, might improve subsequent adherence after stressful cancer diagnoses but not for patients with bipolar and psychotic disorders at risk of poor access and nonadherence. MATERIALS AND METHODS: We included 21,894 women aged ≥ 68 years at their first surgically treated stage I-IV estrogen receptor-positive breast cancer (2007-2013) from the Surveillance, Epidemiology, and End Results-Medicare data set, of whom 5.8% had bipolar or psychotic disorders. We required continuous fee-for-service Medicare (parts A and B) data for ≥ 36 months before and 18 months after the cancer diagnosis. The medication regimen factors in the part D claims for 4 months before included the number of all medications used, pharmacy visits, and administration complexity (medication regimen complexity index subscale). Cox regression analysis was used to model the time to initiation and discontinuation, with longitudinal linear regression for adherence to endocrine therapy. RESULTS: Women with more frequent previous medication use and pharmacy visits were more likely to initiate, 4+ medications and 2+ visits versus no medication (hazard ratio [HR], 1.47; 95% confidence interval [CI], 1.33-1.63), to adhere (6.0%; 95% CI, 4.3-7.6), and to continuously use their endocrine therapy (discontinuation HR, 0.48; 95% CI, 0.39-0.59). Medication administration complexity had modest effects. Difficult medication regimens were more common for patients with bipolar and psychotic disorders but had no statistically significant effects. CONCLUSIONS: Experience with frequent previous medication use and pharmacy visits might increase the likelihood of endocrine therapy use for most patients but not for those with bipolar and psychotic disorders.