Racial/Ethnic Differences in the Use and Discontinuation of Adjuvant Endocrine Therapy by Hormone-Receptor Status in Association with Mortality among Breast Cancer Patients Enrolled in Medicare Part D

Abstract

Abstract Purpose: To determine whether racial/ethnic differences in the use and discontinuation of adjuvant endocrine therapy (AET) differed by hormone-receptor status and was associated with an increased risk of mortality. Methods: We used the SEER/Medicare dataset to conduct a retrospective cohort study of women diagnosed with stage 0-IV breast cancer from 2007–2009 enrolled in Medicare Part D. Women were stratified based on tumor stage and hormone-receptor status (positive, negative, unknown). We performed multivariable logistic regression to assess racial differences in the odds of AET initiation and two Cox proportional hazards models to determine the risk of AET discontinuation and overall mortality. Discontinuation was defined as ≥120 consecutive days without AET medication. All analyses were adjusted for sociodemographic, comorbidities, treatment (surgery, chemotherapy, radiotherapy), and prognostic factors (tumor stage, size, grade, lymph node involvement). Results: Of the 19,960 women diagnosed with breast cancer, 59.3% initiated AET within 12 months of diagnosis. Among women with hormone receptor-positive breast cancer 70.6% initiated AET compared to 20.7% of women with hormone receptor-negative or unknown. Among women with hormone-positive stage I–III breast cancer, blacks were less likely to discontinue AET compared to non-Hispanic whites (HR: 0.89, 95% CI 0.80–0.98). Among women diagnosed with stage IV, hormone receptor-positive breast cancer, Hispanic women were more likely to discontinue AET compared to non-Hispanic whites (HR: 1.68, 95% CI: 1.01–2.78). Women who initiated with the aromatase inhibitors had a 12% increased risk of discontinuation compared to women who initiated with tamoxifen (HR: 1.12, 95% CI 1.05–1.20). In all racial/ethnic groups, regardless of stage and hormone-receptor status, discontinuation of AET was associated with a significantly higher risk of all-cause mortality (HR: 1.72, 95% CI: 1.54–1.93). Conclusions: Over two-third of patients with hormone receptor-positive breast cancer initiated AET and a substantial proportion of hormone receptor-negative women did as well. Discontinuation of AET was associated with a significantly higher risk of all-cause mortality regardless of hormone status and stage.