Background: Racial minorities experience disparities in receipt of cancer treatment and survival. The optional Medicaid expansion provision of the Affordable Care Act provided federal funding to participating states to improve healthcare access for disadvantaged populations by expanding Medicaid eligibility criteria. This study aimed to investigate the effect of Medicaid expansion on racial disparities in mortality among patients with gastrointestinal malignancies. Methods: A cross-sectional cohort study of patients with pancreatic ductal adenocarcinoma (PDAC), colorectal cancer (CRC), and gastric adenocarcinoma (GC) of any stage was conducted using the National Cancer Database (2009-2019). Difference-in-difference analysis (DID) was performed to compare adjusted 2-year mortality separately among Black and White patients residing in Medicaid expansion states (MES) and non-expansion states (non-MES) before (2009-2013) and after (2014-2019) expansion. Differences in receipt of surgery and chemotherapy were also evaluated. Results: A total of 86,052 patients were included for analysis, including 19,188 patients with PDAC, 60,404 with CRC, and 6,460 with GC. Two-year mortality decreased among Black patients with PDAC residing in MES compared to non-MES following expansion (DID -9.4%, p<0.001) (Table). Mortality also decreased among Black and White patients with CRC in MES compared to non-MES following expansion (DID -4.2%, p < 0.001 and -2.9%, p = 0.047). Among patients with GC, Black patients in MES experienced a marked reduction in mortality compared to non-MES (DID -7.7%, p = 0.07). Both Black and White stage 3-4 PDAC patients had an increase in receipt of chemotherapy in MES following expansion (DID 3.7%, p=0.28 and DID 2.7%, p=0.20). Rates of surgery, but not chemotherapy receipt, increased among Black patients with stage 4 CRC in MES following expansion (DID 5.7%, p=0.03 and 1.0%, p=0.66, respectively). A greater increase in receipt of chemotherapy was observed among Black patients with stage 4 GC in MES than in non-MES (DID 11%, p=0.06). Conclusions: Medicaid expansion was associated with a greater reduction in 2-year mortality rates for Black patients residing in MES than for those in non-MES. Existing racial disparities in mortality remained the same or worsened in non-MES but in almost all cases were mitigated in MES following Medicaid expansion.

*Difference in difference (DID); colorectal cancer (CRC).