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Racial Differences in Adjuvant Endocrine Therapy Use and Discontinuation in Association with Mortality among Medicare Breast Cancer Patients by Receptor Status

Background: There are racial disparities in breast cancer mortality. Our purpose was to determine whether racial/ethnic differences in use and discontinuation of adjuvant endocrine therapy (AET) differed by hormone receptor status and whether discontinuation was associated with mortality. Methods: We conducted a retrospective cohort study with SEER/Medicare dataset of women age ≥65 years diagnosed with stage I–III breast cancer in Medicare Part-D from 2007 to 2009, stratified by hormone receptor status. We performed multivariable logistic regressions to assess racial differences for the odds of AET initiation and Cox proportional hazards models to determine the risk of discontinuation and mortality. Results: Of 14,902 women, 64.5% initiated AET <12 months of diagnosis. Among those with hormone receptor–positive cancer, 74.8% initiated AET compared with 5.6% of women with negative and 54.0% with unknown-receptor status. Blacks were less likely to initiate [OR, 0.76; 95% confidence interval (CI), 0.66–0.88] compared with whites. However, those with hormone receptor–positive disease were less likely to discontinue (HR, 0.89; 95% CI, 0.80–0.98). Women who initiated with aromatase inhibitors had increased risk of discontinuation compared with women who initiated tamoxifen (HR, 1.12; 95% CI, 1.05–1.20). Discontinuation within 12 months was associated with higher risk of all-cause (HR, 1.75; 95% CI, 1.74–2.00) and cancer-specific mortality (HR, 2.76; 95% CI, 1.74–4.38) after controlling for race/ethnicity. Conclusions: There are racial/ethnic differences in AET use and discontinuation. Discontinuing treatment was associated with higher risk of all-cause and cancer-specific mortality regardless of hormone receptor status. Impact: This study underscores the need to study factors that influence discontinuation and the survival benefits of receiving AET for hormone receptor–negative breast cancer. Cancer Epidemiol Biomarkers Prev; 26(8); 1266–75. ©2017 AACR.