Traffic-related air pollution and breast cancer risk: a systematic review and a meta-analysis of observational studies

Abstract

BACKGROUND AND AIM: Association of breast cancer risk with air pollution exposure, in particular pollution emitted by traffic exhaust has been investigated but current epidemiological evidence remains inconclusive and methodologies of exposure assessment varied. To systematically review the scientific literature on breast cancer risk and indicators of traffic-related air pollution, e.g. distance from roadways or traffic volume of nearby roadways as well as pollutants from motor vehicle emission and provide meta-analytic estimates of the association between breast cancer and exposure to nitrogen oxides (NOx) and nitrogen dioxides (NO2), the main markers of traffic. METHODS: We systematically reviewed the literature on exposure to traffic-related air pollution and breast cancer risk and conducted a random-effects meta-analysis of observational studies investigating the association between exposure to NO2 and NOx and breast cancer risk. RESULTS:We reviewed six case-control and 11 cohort studies that used different exposure assessment methods and time periods of traffic emissions. While, individual studies provided little evidence of an association between different indicators of traffic-related air pollution and breast cancer risk, the meta-analysis on NO2 (based on three case-control and seven cohort studies) indicated a borderline association (pooled relative risk, RR per 10 µg/m3 of NO2: 1.01; 95% confidence interval, CI: 1.00, 1.03; p=0.03). No significant association between NOx and breast cancer was found on the basis of three cohorts (RR: 1.02; 95%CI: 0.99, 1.05; for an increase of 10 µg/m3 of NOx). CONCLUSIONS:Since traffic is the major contributor to NO2 concentration and is responsible for high concentration observed near busy roads, our findings suggest that traffic-related air pollution is likely to increase breast cancer incidence and to provide additional support for the carcinogenicity of air pollution. KEYWORDS: Breast cancer, epidemiology, air pollution, traffic, nitrogen dioxides, meta-analysis