Socioeconomic Disparities in Mortality Among Women With Incident Breast Cancer Before and After Implementation of Medicare Part D

BACKGROUND: Breast cancer patients exhibit survival disparities based on socioeconomic status (SES). Disparities may be attributable to access to expensive oral endocrine agents. OBJECTIVES: Define recent socioeconomic disparities in breast cancer survival and determine whether these improved after implementation of the Medicare Part D program. DESIGN: Difference-in-difference natural experiment of women diagnosed and treated before or after implementation of Medicare Part D. SUBJECTS: Female Medicare beneficiaries with early-stage breast cancer: 54,772 diagnosed in 2001 and 46,371 in 2007. MEASURES: SES was based on Medicaid enrollment and zip code per capita income, all-cause mortality from Medicare, and cause of death from National Death Index. RESULTS: Among women diagnosed pre-Part D, 40.5% of poor beneficiaries had died within 5 years compared with 20.3% of high-income women (P<0.0001). Post-Part D, 33.6% of poor women and 18.4% of high-income women died by 5 years. After adjustment for potential confounders, improvement in all-cause mortality post-Part D was greater for poorer women compared with more affluent women (P=0.002). However, absolute improvement in breast cancer-specific mortality was 1.8%, 1.2%, and 0.8% (P=0.88 for difference in improvement by SES), respectively for poor, near-poor, and high-income women, whereas analogous improvement in mortality from other causes was 5.1%, 3.8%, and 0.9% (P=0.067 for difference in improvement by SES). CONCLUSIONS: Large survival disparities by SES exist among breast cancer patients. The Part D program successfully ameliorated SES disparities in all-cause mortality. However, improvement was concentrated in causes of death other than breast cancer, suggesting remaining gaps in care.