Spillover Effects of Medicaid Expansion on Insurance Coverage, Diagnosis, and Survival Among Low-Income Older Patients With Cancer.

BACKGROUND: Medicaid expansion under the Affordable Care Act primarily benefits adults aged <65 years but may also indirectly benefit individuals aged ≥65 years. This study examines the associations of Medicaid expansion with insurance coverage and cancer outcomes among older patients residing in low-income areas. PATIENTS AND METHODS: Using the National Cancer Database, we identified patients aged ≥65 years, newly diagnosed with cancer 2010-2021, and residing in areas with median household income <200% of the federal poverty level. Using the quasi-experimental difference-in-differences design, multivariable models compared dual Medicare-Medicaid enrollment or Medicaid-only coverage, stage at diagnosis, treatment initiation, and 2-year overall survival before and after Medicaid expansion in expansion versus non-expansion states. RESULTS: Our sample included 1,461,540 patients. Dual Medicare-Medicaid or Medicaid-only coverage increased in Medicaid expansion states (10.3%-11.3%) and decreased in Medicaid non-expansion states (9.4%-8.1%), resulting in a net increase of 1.25 percentage points (ppt; 95% CI, 1.02-1.48). Early-stage cancer diagnoses decreased overall, driven by prostate cancer, but declined less in expansion states than in non-expansion states, with a net adjusted relative increase of 1.00 ppt (95% CI, 0.59-1.41). Such protective effects were stronger for lung/bronchus and head and neck cancers. Treatment initiation within 30 days also decreased less in expansion states than non-expansion states, with a net adjusted increase of 0.74 ppt (95% CI, 0.34-1.14). Two-year overall survival increased more in expansion states (58.8%-62.4%) than non-expansion states (59.2%-62.5%), leading to a net increase of 0.70 ppt (95% CI, 0.35-1.04). Such increase was most notable for stage IV, lung/bronchus, kidney, and bladder cancers. CONCLUSIONS: Medicaid expansion was associated with increased Medicaid coverage, attenuated declines in early-stage diagnosis and timely treatment initiation, and improved survival among low-income older patients with cancer, highlighting important spillover benefits beyond the target population.