Annual cases of colon cancer by age group after Medicaid expansion in the USA in 2014: a difference-in-differences study.

Asiimwe E, May F, Bendavid E. Annual cases of colon cancer by age group after Medicaid expansion in the USA in 2014: a difference-in-differences study. BMJ open. 2025 Jun 23; 15(6):e099058, DOI: 10.1136/bmjopen-2025-099058.

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Abstract:

BACKGROUND: Studies examining the association between Medicaid expansion (ME) under the Affordable Care Act (ACA) and colon cancer incidence have produced mixed results. OBJECTIVE: To re-visit the association between the ACA-ME and annual cases of colon cancer. DESIGN: Difference-in-differences (DiD). SETTING: The primary analyses used data from the National Cancer Database from 2010 to 2018, a hospital-based cancer registry in the USA. We also conducted exploratory analyses using data from the Surveillance, Epidemiology and End Results (SEER) registry. PATIENTS: Patients aged 40 and older with newly diagnosed colon cancer. MEASUREMENTS: The primary outcome was the percent change in colon cancer of all stages. Secondary outcomes were percent changes in stage I and stage IV cases. RESULTS: Among those aged 40-49, we observed a statistically significant greater increase in stage I colon cancer in expansion states relative to non-expansion states (DiD (percent change) 9.7% (95% CI, 2.5% to 17.4%)). In those aged 50-64, we did not observe statistically significant differences between the two state groups in any of the outcomes. Among those aged 65+, we observed a statistically significant relative decrease for all stages in ACA-ME states (-1.0% (95% CI, -1.0% to -3.0%)) and for stage IV (-3.0% (95% CI, -2.0% to -5.0%)). We explored our findings among younger individuals ( < 50) in trend plots comparing annual colorectal cancer cases to percent uninsured using SEER data and observed that increases in cases coincided with declining uninsurance in several states. CONCLUSION: Post-ME, we observed a greater relative increase in colon cancer among those < 50 in expansion states. Our exploratory analyses suggest that fewer barriers to healthcare post-ME may have contributed to these findings; additional studies are needed. We also observed relative decreases in the 65+ age group, corroborating previous reports of spillover benefits in expansion states.