Deprivation and Rurality Mediate Income Inequality's Association with Colorectal Cancer Outcomes.

ABSTRACT

INTRODUCTION: Income inequality is associated with poor health outcomes, but its association with colorectal cancer is not well-studied. The authors aimed to determine the association between income inequality and colorectal cancer incidence/mortality in U.S. counties, and hypothesized that this association was mediated by deprivation. METHODS: The authors performed a cross-sectional study of U.S. counties from 2015-2019 using statewide cancer registries and the Centers for Disease Control and Prevention WONDER database. Generalized linear negative binomial regression was performed in 2024 to estimate the association between Gini coefficient (income inequality) and colorectal cancer incidence/mortality using incidence rate ratios (IRRs) for the entire cohort and stratified by rurality. RESULTS: A total of 697,981 colorectal cancer cases were diagnosed in the 5-year study period. On adjusted regression, for every 0.1 higher Gini coefficient, there was an 11% higher risk of both colorectal cancer incidence and mortality (IRR 1.11, 95%CI 1.03,1.19 and IRR 1.11, 95%CI 1.05, 1.18 respectively). The association between income inequality and incidence/mortality peaked in more rural counties, however there was not an overall dose-dependent relationship between rurality and these associations. Deprivation mediated the association between income inequality and colorectal cancer incidence (indirect effect B coefficient 0.088, p<0.001) and mortality (B coefficient 0.088, p<0.001). The magnitude and direction of the direct, indirect, and total effects differed in each rurality strata. CONCLUSIONS: Much of income inequality's association with colorectal cancer outcomes operates through deprivation. Rural counties have a stronger association between higher income inequality and higher mortality, which works in tandem with deprivation.