Association of medicaid expansion with lung cancer–specific and overall mortality: A difference-in-differences analysis

Introduction Medicaid expansion under the Affordable Care Act (ACA) sought to improve access to timely cancer diagnosis and treatment among low‑income populations. Lung cancer remains the leading cause of cancer-related mortality in the United States, and disparities in outcomes may be sensitive to shifts in insurance coverage. This study evaluates the association between Medicaid expansion and both cancer-specific mortality and overall mortality among adults with lung cancer in California (expansion state) compared with Texas (non-expansion state). Methods We conducted a retrospective cohort study using SEER registry data (2007–2021) including adults aged 18–64 years diagnosed with lung cancer. The study periods were categorized as pre-ACA (2007–2013), washout year (2014), and post-ACA (2015–2021). Difference‑in‑differences (DiD) Cox proportional hazards models estimated the change in the hazard of cancer‑specific and overall mortality in California relative to Texas after Medicaid expansion, adjusting for age, sex, race/ethnicity, stage, county‑level income, and treatment. Subgroup analyses evaluated heterogeneity by race/ethnicity, disease stage, income, and treatment modality. Results Among 119, 937 individuals with lung cancer, 52. 1% resided in California and 47. 8% in Texas; sample distribution remained similar across pre‑ and post‑ACA periods. Medicaid expansion was associated with an 11. 9% reduction in the hazard of cancer‑specific mortality (DiD HR 0. 88; 95% CI, 0. 85–0. 91) and an 11. 4% reduction in the hazard of overall mortality (DiD HR 0. 89; 95% CI, 0. 86–0. 91). Mortality reductions varied across subgroups. Significant improvements were observed among White, Hispanic, and Asian/Pacific Islander patients, while no statistically significant change occurred among Black patients. Greater reductions in the hazard of death were seen among patients with distant-stage disease and those residing in higher‑income areas (≥65, 000). Treatment-stratified models showed decreases in mortality among individuals receiving surgery (10. 2% reduction) and chemotherapy (8. 4% reduction). Conclusion Medicaid expansion was associated with meaningful reductions in lung cancer mortality in California relative to Texas, with benefits concentrated among several racial and clinical subgroups. Persistent null effects among Black patients highlight inequities that insurance expansion alone does not eliminate.