Ambient PM2.5 exposure and cancer incidence in Nigerian adults: A prospective cohort study.

BACKGROUND: Ambient PM2.5 is an IARC Group 1 carcinogen, yet prospective evidence from sub-Saharan Africa remains scarce. We investigated long-term exposure to PM2.5, PM10, and NO₂ and incident cancer risk in a Nigerian adult cohort. METHODS: We studied 5621 adults across Lagos, Kano, and Rivers States with median follow-up of 4.7 years (25,418 person-years). Annual pollutant concentrations were estimated using hybrid satellite-land use regression at 1 km resolution. Incident cancers were confirmed histopathologically. Biomarkers of oxidative stress and inflammation were measured in a subsample. Hazard ratios (HRs) were estimated using Cox regression with mediation analysis. RESULTS: Mean PM2.5 was 50.4 μg/m³ , tenfold above WHO guidelines. A total of 147 incident cancers occurred. Each 10 μg/m³ PM2.5 increment was associated with a 12% increase in all-cancer incidence (HR 1.12; 95% CI: 1.06-1.19). Highest versus lowest PM2.5 quartile had 82% elevated hazard (HR 1.82; 95% CI: 1.29-2.57). Site-specific associations were strongest for lung, breast, and hematopoietic malignancies. Dose-dependent elevations in oxidative stress and inflammatory markers were observed. Mediation analysis indicated this pathway accounted for 41.3% of the total PM2.5-cancer association. CONCLUSIONS: In this first prospective sub-Saharan African cohort, chronic PM2.5 exposure was positively associated with incident cancer risk. Oxidative stress and inflammation mediate a substantial proportion of this association. These findings support integrating air quality monitoring into national cancer control strategies.