Evaluating the role of Medicaid expansion on survival in early-onset colorectal cancer

BACKGROUND: The Affordable Care Act (ACA) expanded Medicaid eligibility to states on staggered timelines, creating a natural experiment to assess health policy effects on colorectal cancer (CRC) outcomes. METHODS: We conducted a retrospective quasi-experimental cohort study using the SEER database (2006 to 2019). Patients with CRC <65 years were included in primary analyses; a EOCRC cohort aged <50 years was examined. States were classified by Medicaid expansion timing, and each expansion group was propensity score-matched against non-expansion controls. The primary analysis used pooled Bayesian difference-in-differences survival models with censoring at 36 months, with sensitivity analyses at 60 months and uncapped follow-up. Secondary Bayesian logistic models evaluated stage at diagnosis and receipt of surgical resection. Results are reported as hazard ratios (HR) or odds ratios (OR) with 95% credible intervals (CrI) and posterior probabilities of benefit. RESULTS: In pooled analyses among patients younger than 65 years, Medicaid expansion was associated with reduced mortality (36-month HR = 0.86; 95%CrI, 0.81 to 0.92; P(HR < 1)>0.999), with consistent findings across follow-up endpoints. Survival benefit was larger among patients with early-onset CRC (age <50 years). No consistent association was observed among Medicare-eligible patients aged ≥65. Medicaid expansion was not associated with population-level shifts in stage at diagnosis or increased surgical resection. CONCLUSION: Medicaid expansion under the ACA was associated with a high probability of improved CRC survival among non-Medicare-eligible adults, including patients with early-onset disease. Survival gains occurred without corresponding changes in stage or surgical treatment, suggesting benefits mediated through improved access, continuity, and delivery of cancer care.