Long-term exposure to ambient air pollution and incidence of brain tumor: the European Study of Cohorts for Air Pollution Effects (ESCAPE)

BACKGROUND: Epidemiological evidence on the association between ambient air pollution and brain tumor risk is sparse and inconsistent. METHODS: In 12 cohorts from 6 European countries, individual estimates of annual mean air pollution levels at the baseline residence were estimated by standardized land-use regression models developed within the ESCAPE and TRANSPHORM projects: particulate matter (PM) ≤2.5, ≤10, and 2.5–10 μm in diameter (PM(2.5), PM(10), and PM(coarse)), PM(2.5) absorbance, nitrogen oxides (NO(2) and NO(x)) and elemental composition of PM. We estimated cohort-specific associations of air pollutant concentrations and traffic intensity with total, malignant, and nonmalignant brain tumor, in separate Cox regression models, adjusting for risk factors, and pooled cohort-specific estimates using random-effects meta-analyses. RESULTS: Of 282194 subjects from 12 cohorts, 466 developed malignant brain tumors during 12 years of follow-up. Six of the cohorts also had data on nonmalignant brain tumor, where among 106786 subjects, 366 developed brain tumor: 176 nonmalignant and 190 malignant. We found a positive, statistically nonsignificant association between malignant brain tumor and PM(2.5) absorbance (hazard ratio and 95% CI: 1.67; 0.89–3.14 per 10(–5)/m(3)), and weak positive or null associations with the other pollutants. Hazard ratio for PM(2.5) absorbance (1.01; 0.38–2.71 per 10(–5)/m(3)) and all other pollutants were lower for nonmalignant than for malignant brain tumors. CONCLUSION: We found suggestive evidence of an association between long-term exposure to PM(2.5) absorbance indicating traffic-related air pollution and malignant brain tumors, and no association with overall or nonmalignant brain tumors.