Ambient air pollution and primary liver cancer incidence in four European cohorts within the ESCAPE project.

BACKGROUND: Tobacco smoke exposure increases the risk of cancer in the liver, but little is known about the possible risk associated with exposure to ambient air pollution. OBJECTIVES: We evaluated the association between residential exposure to air pollution and primary liver cancer incidence. METHODS: We obtained data from four cohorts with enrolment during 1985-2005 in Denmark, Austria and Italy. Exposure to nitrogen oxides (NO2 and NOX), particulate matter (PM) with diameter of less than 10µm (PM10), less than 2.5µm (PM2.5), between 2.5 and 10µm (PM2.5-10) and PM2.5 absorbance (soot) at baseline home addresses were estimated using land-use regression models from the ESCAPE project. We also investigated traffic density on the nearest road. We used Cox proportional-hazards models with adjustment for potential confounders for cohort-specific analyses and random-effects meta-analyses to estimate summary hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS: Out of 174,770 included participants, 279 liver cancer cases were diagnosed during a mean follow-up of 17 years. In each cohort, HRs above one were observed for all exposures with exception of PM2.5 absorbance and traffic density. In the meta-analysis, all exposures were associated with elevated HRs, but none of the associations reached statistical significance. The summary HR associated with a 10-µg/m3 increase in NO2 was 1.10 (95% confidence interval (CI): 0.93, 1.30) and 1.34 (95% CI: 0.76, 2.35) for a 5-µg/m3 increase in PM2.5. CONCLUSIONS: The results provide suggestive evidence that ambient air pollution may increase the risk of liver cancer. Confidence intervals for associations with NO2 and NOX were narrower than for the other exposures.