BACKGROUND: Disparities exist in access to high-volume surgeons, who have better outcomes after thyroidectomy. The association of the Affordable Care Act's Medicaid expansion with access to high-volume thyroid cancer surgery centers remains unclear.

METHODS: The National Cancer Database was queried for all adult thyroid cancer patients diagnosed from 2010 to 2016. Hospital quartiles (Q1-4) defined by operative volume were generated. Clinicodemographics and adjusted odds ratios for treatment per quartile were analyzed by insurance status. An adjusted difference-in-differences analysis examined the association between implementation of the Affordable Care Act and changes in payer mix by hospital quartile.

RESULTS: In total, 241,448 patients were included. Medicaid patients were most commonly treated at Q3-Q4 hospitals (Q3 odds ratios 1.05, P = .020, Q4 1.11, P < .001), whereas uninsured patients were most often treated at Q2-Q4 hospitals (Q2 odds ratios 2.82, Q3 2.34, Q4 2.07, P < .001). After expansion, Medicaid patients had lower odds of surgery at Q3-Q4 compared with Q1 hospitals (odds ratios Q3 0.82, P < .001 Q4 0.85, P = .002) in expansion states, but higher odds of treatment at Q3-Q4 hospitals in nonexpansion states (odds ratios Q3 2.23, Q4 1.86, P < .001). Affordable Care Act implementation was associated with increased proportions of Medicaid patients within each quartile in expansion compared with nonexpansion states (Q1 adjusted difference-in-differences 5.36%, Q2 5.29%, Q3 3.68%, Q4 3.26%, P < .001), and a decrease in uninsured patients treated at Q4 hospitals (adjusted difference-in-differences -1.06%, P = .001).

CONCLUSIONS: Medicaid expansion was associated with an increased proportion of Medicaid patients undergoing thyroidectomy for thyroid cancer in all quartiles, with increased Medicaid access to high-volume centers in expansion compared with nonexpansion states.