Association between fine particulate matter exposure and colorectal cancer mortality by age at diagnosis: Insights from county-level analysis in the United States.

3632 Background: Colorectal cancer (CRC) remains a leading cause of cancer mortality in the U.S., with environmental factors like air pollution potentially contributing to mortality. This study examines the association between fine particulate matter (PM2.5) exposure and CRC mortality rates, stratified by average-onset (aoCRC [≥50 years at diagnosis]) and early-onset (eoCRC [ < 50 years at diagnosis]) cases. Methods: Age-adjusted county CRC mortality data (1999–2020, n = 2981 counties) were obtained from CDC Underlying Cause of Death (ICD-10: C18-C19 [excluding C18.1], C20), while 1999-2019 PM2.5 estimates (ug/m3), derived from Atmospheric Composition Analysis Group data, were mapped to U.S. county boundaries using R v.4.3.2. Covariates were derived from Census American Community Survey (ACS) 5-year estimates, CDC data, and County Health Rankings (CHR) data and included county-level area deprivation index (ACS), non-Hispanic Black % (ACS), Hispanic % (ACS), obesity prevalence (CDC), smoking prevalence (CHR), binge alcohol consumption (CHR), and uninsured % (ACS). Negative binomial count models were fit to explore associations between PM2.5 and CRC mortality rates, adjusted for covariates. Deviance R 2 was computed to examine model fits. Results: We found that for every 1% increase in PM2.5 exposure, aoCRC mortality increased by 0.98% (p < 0.001) and eoCRC mortality increased by 0.24% (p = 0.435), after adjustment for covariates. Deviance R 2 values indicated that PM2.5 and covariates explained 32.0% and 37.0% of the deviance in aoCRC and eoCRC mortality, respectively. Conclusions: PM2.5 exposure was a significant predictor of CRC mortality, but only for aoCRC cases. Air pollution and other covariates accounted for roughly one-third of the county-level deviance, suggesting the influence of additional factors. Systemic and individual-level interventions to reduce air pollution exposure may mitigate CRC mortality disparities in older populations. Further studies are needed to explore other potential contributors to CRC mortality.