Abstract
Purpose Previous studies suggest that adherence to adjuvant endocrine therapy (AET) for patients with breast cancer is suboptimal, especially among minorities, and is associated with out-of-pocket medication costs. This study aimed to determine whether there are racial/ethnic differences in 1-year adherence to AET and whether out-of-pocket costs explain the racial/ethnic disparities in adherence. Methods This retrospective cohort study used the SEER-Medicare linked database to identify patients ≥ 65 years of age with hormone receptor-positive breast cancer who were enrolled in Medicare Part D from 2007 to 2009. The cohort included non-Hispanic whites, blacks, Hispanics, and Asians. Out-of-pocket costs for AET medications were standardized for a 30-day supply. Adherence to tamoxifen, aromatase inhibitors (AIs), and overall AET (tamoxifen or AIs) was assessed using the medication possession ratio (≥ 80%) during the 12-month period. Results Of 8,688 patients, 3,197 (36.8%) were nonadherent to AET. Out-of-pocket costs for AET medication were associated with lower adjusted odds of adherence for all four cost categories compared with the lowest category of ≤ $2.65 ( P < .01). In the univariable analysis, Hispanics had higher odds of adherence to any AET at initiation (OR, 1.30; 95% CI, 1.07 to 1.57), and blacks had higher odds of adherence to AIs at initiation (OR, 1.27; 95% CI, 1.04 to 1.54) compared with non-Hispanic whites. After adjusting for copayments, poverty status, and comorbidities, the association was no longer significant for Hispanics (OR, 0.95; 95% CI, 0.78 to 1.17) or blacks (OR, 0.96; 95% CI, 0.77 to 1.19). Blacks had significantly lower adjusted odds of adherence than non-Hispanic whites when they initiated AET therapy with tamoxifen (OR, 0.54; 95% CI, 0.31 to 0.93) after adjusting for socioeconomic, clinic, and prognostic factors. Conclusion Racial/ethnic disparities in AET adherence were largely explained by women's differences in socioeconomic status and out-of-pocket medication costs.