County-level residential radon exposure, testing patterns, and cancer incidence in Michigan.

e22542 Background: Radon is a well-established lung carcinogen and the second leading cause of lung cancer in the United States. Population-level studies evaluating radon exposure and cancer incidence have yielded inconsistent results, potentially due to heterogeneity in exposure assessment and testing practices. We evaluated county-level associations between residential radon exposure, testing patterns, and cancer incidence in Michigan. Methods: Residential radon test results (~99,300 tests) from the Michigan Department of Environment, Great Lakes, and Energy were aggregated to the county level. Radon exposure was assessed using mean concentration, percentage of tests exceeding the EPA action level, and EPA radon category (Levels 1–2 vs Level 3 reference). Age-adjusted cancer incidence rates (2017–2021) were obtained from NCI State Cancer Profiles. Negative binomial regression models evaluated associations between radon measures and incidence of 11 cancer types at the county level in Michigan, with and without adjustment for county-level smoking prevalence, median household income, percent male, percent age ≥65 years, and percent Black population. Correlation and rural–urban analyses were performed. Results: After covariate adjustment, no significant association was observed between any radon metric and lung cancer incidence (all adjusted p > 0.05). Null associations were also observed for other evaluated cancer types. Average radon levels did not differ between rural and urban counties. A modest positive correlation was observed between the percentage of tests exceeding the EPA action level and median household income (r = 0.22, p = 0.04). Conclusions: County-level residential radon exposure was not independently associated with cancer incidence after adjustment for key sociodemographic and behavioral factors. The association between elevated radon test prevalence and higher income suggests socioeconomic disparities in radon testing that may obscure true exposure patterns in lower-income communities, underscoring the need for equitable radon screening and mitigation strategies in cancer prevention.