Importance: Having health insurance is a strong determinant of cancer outcomes in the United States, and Medicaid expansion under the Patient Protection and Affordable Care Act (ACA) may have reduced the prevalence of uninsured patients. Prior research has only assessed the aggregate effects of expansions, and little is known about changes in uninsured patients by state and key sociodemographic groups, including sex, race/ethnicity, census tract-level poverty, and rurality.

Objective: To examine changes in the percentage of uninsured patients and stage at diagnosis among nonelderly patients with cancer by state and key sociodemographic groups after implementation of the ACA.

Design, setting, and participants: This study used difference-in-differences analysis to determine the percentage of uninsured patients and early-stage cancer diagnoses among patients aged 18 to 64 years from the population-based cancer registries of 40 states before (January 1, 2010, to December 31, 2013) and after (January 1, 2014, to December 31, 2014) the ACA Medicaid expansion. Data analysis was performed from November 2017 to April 2018.

Main outcomes and measures: Changes in the percentage of uninsured patients and early-stage diagnoses.

Results: A total of 2 471 154 patients (mean age, 52.7 years; age range, 18-64 years; 51.4% female; 70.9% non-Hispanic white) were included from Medicaid expansion (n = 1 234 156) and nonexpansion (n = 1 236 998) states. In 2014, the percentage of uninsured patients decreased in almost all states. However, decreases were greater in expansion than nonexpansion states and were greatest in expansion states with high baseline uninsured rates. For example, the percentage of uninsured patients decreased from 8.3% before implementation of the ACA to 2.1% (-6.2 difference) after implementation of the ACA in the expansion state of Kentucky compared with 9.1% to 7.5% (-1.5 difference) in the nonexpansion state of Tennessee. In expansion states, the decreases in the percentage of uninsured patients were higher among minorities and patients in high-poverty or rural areas, diminishing or eliminating disparities. In contrast, sociodemographic disparities in the percentage of uninsured patients remained high in nonexpansion states. Stage at diagnosis shifted slightly to earlier stage for most cancer types in Medicaid expansion states.

Conclusions and relevance: This study found state variation in reductions in the percentage of uninsured patients among nonelderly patients with cancer after implementation of the ACA, with larger decreases in expansion than nonexpansion states. Disparities in the percentage of uninsured patients by race/ethnicity, census tract-level poverty, and rurality were diminished or eliminated in Medicaid expansion states but remained high in nonexpansion states, highlighting the promising role of Medicaid expansion in reducing disparities among sociodemographic subpopulations. Future studies should monitor changes in cancer presentation, treatment, and outcomes after implementation of the ACA.