The Impact of Early Medicaid Expansions on Breast Cancer Stage at Diagnosis in California
Data on breast cancer cases in California come from the Surveillance, Epidemiology, and End Results Program (SEER) cancer registry. The SEER data include information on patient demographics (age, sex, race, ethnicity, and marital status), cancer site, diagnosis date, stage at diagnosis, and grade or size of the tumor, and geographic areas (including SEER registry and county). The Area Health Resources File (AHRF) dataset is used to control for county level factors that may impact breast screening among Medicaid-eligible individuals. Our population of interest comprised females aged 19-64 years with breast cancer diagnosed between 2000 and 2012. We also categorize counties within California as low-income versus medium- or high-income based on median household income to explore heterogeneous effects across areas likely to experience a greater impact from increases in Medicaid eligibility. Our primary outcome of interest is an indicator of whether the breast cancer diagnosis was made at a late stage of disease. We used SEER summary staging criteria and defined early stage as in situ or localized breast cancer and late stage as regional or distant. Of 196,739 breast cancer diagnoses in California reported in SEER over this time period, 32% were late stage. Preliminary results suggest that breast cancer diagnoses were significantly less likely to be late stage in the years after expansion relative to the pre-expansion period, conditional on individual and county characteristics. Additional analyses will exploit variation both within California and across states to estimate the impact of coverage expansions. To our knowledge, this is the first study to estimate the effect of Medicaid expansions on breast cancer stage at diagnosis, and will have important implications for understanding the role of coverage in impacting cancer outcomes.