Poster #67 - Medicaid Expansion and Cancer Outcomes: Heterogeneous Effects by Geographic Access to Oncology Centers

• In Event: Friday Poster Reception

Abstract

This study examines the causal effects of Medicaid expansion on cancer outcomes and investigates how these effects vary depending on geographic access to oncology centers. Under the Affordable Care Act (ACA), states were given the option to expand Medicaid eligibility to low-income adults, but implementation varied. For instance, Georgia did not adopt the expansion, whereas California implemented it in 2014, extending Medi-Cal eligibility to adults with incomes up to 138% of the federal poverty level, including previously ineligible childless adults.

The policy divergence between Georgia and California offers a quasi-experimental setting for estimating the causal impact of Medicaid expansion on cancer outcomes. Using a difference-in-difference approach, the analysis compared cancer-related outcomes before and after the 2014 policy implementation, treating Georgia as the non-expansion control group and California as the expansion treatment group. The identification strategy relies on the assumption of parallel pre-expansion trends between the two states. Linked SEER-Medicaid data, a nationally representative dataset maintained by the National Cancer Institute and covering cancer cases from 1999 to 2020 (N > 1,900,000) was utilized for the analysis. Key outcomes include stage at diagnosis, time for diagnosis to treatment, and all-cause mortality across five major cancer sites: breast, lung, colorectal, prostate, and pancreatic.

Furthermore, this study assesses the heterogeneous effects of Medicaid expansion across areas with varying levels of geographic access to oncology services. Limited spatial access has been associated with delayed and more advanced-stage diagnoses. Yet, its role in moderating Medicaid expansion effects remains underexplored. To address this gap, a geospatial dataset of cancer care facilities was developed using OpenStreetMap (OSM) and the Overpass API. These facilities were geocoded and linked to patient residential census tracts to calculate travel distances and classify levels of geographic access.

Using these geographic access measures, the analysis examines how the effect of Medicaid expansion differs by proximity to cancer care. Preliminary findings suggest that Medicaid expansion is associated with improved cancer outcomes, including earlier-stage diagnoses, reduced time to treatment, and lowering mortality. Notably, these effects are more evident in areas with greater geographic access to oncology centers. Results hold across subgroup analyses comparing Atlanta and Los Angeles and remain robust to propensity score-based adjustments.

This study contributes to the existing literature by providing updated national evidence and offering new insights into how geographic access mitigates the impact of Medicaid expansion on cancer outcomes. The analysis extends beyond insurance coverage alone by empirically demonstrating the intersection between Medicaid coverage and geographic access in shaping cancer outcomes. Findings from this research are intended to support policy and planning initiatives that address cancer care disparities, especially in underserved and geographically isolated communities.

Author

• Kristine Jenny Hahm, University of Texas, Dallas
  Presenting Author