Medicaid Expansion and Mortality Among Patients With Colorectal Cancer.

IMPORTANCE: Medicaid expansion under the Patient Protection and Affordable Care Act (ACA) substantially increased insurance coverage among adults with low income, yet its impact on colorectal cancer survival and underlying mechanisms remains incompletely defined. OBJECTIVE: To evaluate the association between Medicaid expansion and overall survival among adults with colorectal cancer and to assess heterogeneity by race and ethnicity, disease stage, and potential mechanisms, including stage at diagnosis and treatment use. DESIGN, SETTING, AND PARTICIPANTS: This retrospective cohort study used data from the National Cancer Database (2006-2021). Adults aged 40 to 64 years with newly diagnosed colorectal cancer were included. A difference-in-differences design compared outcomes between Medicaid expansion and nonexpansion states in pre-ACA (2006-2013) and post-ACA (2014-2021) periods. The data were analyzed between January 18 and March 30, 2026. EXPOSURE: Residence in a Medicaid expansion vs nonexpansion state. MAIN OUTCOMES AND MEASURES: Overall mortality was the primary outcome. Secondary outcomes included stage at diagnosis and treatment use. Adjusted hazard ratios (HRs), relative hazard reductions, and absolute differences were estimated. RESULTS: Among 658 593 adults (mean [SD] age, 54.9 [6.3] years; 366 800 male [55.7%]), Medicaid expansion was associated with lower overall mortality (difference-in-differences HR, 0.94 [95% CI, 0.93-0.95]), corresponding to a 6.3% (95% CI, 5.1%-7.5%) relative reduction in overall mortality. The largest survival association was observed among Hispanic patients (HR, 0.77 [95% CI, 0.75-0.80]). Benefits were also seen across all disease stages, with the most pronounced association observed in stage IV disease (HR, 0.88 [95% CI, 0.83-0.94]). Expansion was associated with an increase of 2.13 percentage points in early-stage diagnosis (95% CI, 1.60-2.65 percentage points) and increased surgical treatment (1.54 percentage points [95% CI, 1.19-1.90 percentage points]). CONCLUSIONS AND RELEVANCE: This cohort study of adults with colorectal cancer found that Medicaid expansion was associated with improved survival. Observed shifts in stage at diagnosis and treatment use were consistent with but could not establish, given the available data, earlier detection and improved access to definitive care as mechanisms. Persistent heterogeneity across populations highlights the need for additional strategies to ensure equitable cancer outcomes.