Medicaid Expansion and Overall Mortality Among Women With Breast Cancer.

Importance: Medicaid expansion under the Patient Protection and Affordable Care Act (ACA) was designed to improve access to care and reduce health disparities. Its association with breast cancer mortality and related disparities remains unclear. Objectives: To evaluate the association between Medicaid expansion and overall mortality among women with breast cancer and to assess whether survival differs by race and ethnicity, disease stage, income, and treatment modality. Design, Setting, and Participants: This retrospective, hospital-based cohort study used a National Cancer Database cohort of 1 595 845 women aged 40 to 64 years with breast cancer who received a diagnosis from January 1, 2006, to December 31, 2021. States were classified as either Medicaid expansion or nonexpansion states. Statistical analyses were performed between January and July 2025. Exposure: Residence in a state that implemented Medicaid expansion by January 2014. Main Outcomes and Measures: The primary outcome was all-cause mortality. Policy effects were derived from difference-in-differences Cox proportional hazards regression models, reported as hazard ratios (HRs) and percentage change in hazard. Effect modification by race and ethnicity, disease stage, zip code-level income, and treatment was tested with 3-way interactions and joint Wald χ2 tests. Results: Of 1 595 845 women with breast cancer (mean [SD] age, 53.7 [6.8] years), 922 862 (57.8%) lived in early-expansion states, and 672 983 (42.2%) in nonexpansion states. Medicaid expansion was associated with lower overall mortality (HR, 0.95; 95% CI, 0.95-0.96; P < .001), a 4.8% relative hazard reduction vs nonexpansion. Hazard reductions were -3.4% (95% CI, -4.2% to -2.6%) for non-Hispanic White women, -4.3% (95% CI, -6.3% to -2.2%) for non-Hispanic Black women, and -19.0% (95% CI, -20.8% to -17.2%) for Hispanic women; associations for non-Hispanic women of other race or ethnicity were not significant. Lower mortality was most pronounced among patients with metastatic disease (-13.9%; 95% CI, -20.0% to -7.2%), those in the highest-income neighborhoods (-9.7%; 95% CI, -10.7% to -8.7%), and those receiving immunotherapy (-24.1%; 95% CI, -28.6% to -19.3%). Conclusions and Relevance: The findings of this cohort study suggest that Medicaid expansion under the ACA was associated with lower overall mortality among women aged 40 to 64 years with breast cancer. Benefits were uneven, underscoring persistent racial and ethnic and socioeconomic disparities and the need for targeted interventions.