Compared to cancers detected early, distant stage cancers are associated with lower survival, diminished quality of life, and higher costs. Evidence suggests that greater access to comprehensive health insurance (i.e., Medicare) improved early detection. Yet, few studies have evaluated the effect of Medicare coverage across cancers or factors influencing healthcare use. To address this gap, I analyzed 35 years of population-based cancer registry data from the Surveillance Epidemiology and End Results program for eight common cancers: Oral, Digestive, Respiratory, Skin, Genital, Urinary, Endocrine, and Breast. I leverage the subjective threshold determining Medicare’s eligibility to estimate Medicare’s effect on the probability of a distant diagnosis by analyzing data-driven, Robust Non-Parametric Regression Discontinuity models. Medicare was associated with reduced proportion of distant diagnoses for five common cancers. The proportion of distant cancers declined by 1.7-percentage points for digestive cancers (p < 0.01), 1.6-percentage points for respiratory cancers (p < 0.01), 0.5-percentage points for genital cancers (p < 0.05), 1.4-percentage points for urinary cancers (p < 0.01), and 0.8-percentage points for female breast cancers (p < 0.01). Most estimates were consistent across gender, but Medicare was only associated with declined distant-stage diagnoses for patients in urban and metro regions. As policymakers debate expanding Medicare eligibility and benefits, this study reaffirms that Medicare coverage generally improves cancer outcomes. These results stress the importance of healthcare access, but also reveal the limitations of insurance expansion policies for patients without available physicians and for cancers without standard physician screening protocols
