Medicaid Expansion and Overall Mortality in Lung, Breast, and Colorectal Cancer: A Difference-in-Differences Study

BackgroundMedicaid expansion under the Affordable Care Act (ACA) was designed to improve access to care for low-income adults, but its impact on cancer survival may vary across diseases depending on differences in screening, stage at diagnosis, and treatment pathways.MethodsWe conducted a retrospective cohort study using the National Cancer Database to identify adults aged 40-64 years diagnosed with lung, breast, or colorectal cancer between 2007 and 2021. States were classified by Medicaid expansion status, and diagnoses were grouped into pre-ACA (2007-2013) and post-ACA (2015-2021) periods, with 2014 treated as a washout year. The primary outcome was overall mortality. Difference-in-differences Cox proportional hazards models with robust standard errors were used to estimate associations, adjusting for demographic, clinical, insurance, and facility characteristics.ResultsThe cohort included 2 739 101 patients: 631 721 (23.1%) with lung cancer, 1 581 956 (57.8%) with breast cancer, and 516 424 (18.9%) with colorectal cancer. Medicaid expansion was associated with a 2.9% relative reduction in overall mortality compared with non-expansion states (difference-in-differences hazard ratio [HR], 0.97; 95% CI, 0.97-0.98). The magnitude varied by cancer type, with the largest reduction for lung cancer (HR, 0.94), followed by colorectal (HR, 0.97) and breast cancer (HR, 0.98). Substantial heterogeneity was observed by ethnicity, with the largest reduction among Hispanic patients (HR, 0.83; 95% CI, 0.82-0.85).ConclusionMedicaid expansion was associated with modest reductions in overall mortality, with variation across cancer types reflecting disease-specific factors, and the largest gains observed among lung cancer and Hispanic patients.