Long-term exposure to air pollution and the risk of non-lung cancer: a meta-analysis of observational studies

Several meta-analyses of observational studies report a long-term correlation between air pollution and the risk of cancer, particularly lung carcinoma. The aim of this study was to review and quantify evidence for an association between air pollution and the risk of developing non-lung cancers.

We searched PubMed, EMBASE, Cochrane Library, and the reference lists of the included studies as well as those recorded in previous meta-analyses conducted before January 2019. A random-effects model was used to derive overall risk estimates per pollutant.

A total of 20 studies, including 5 case-control and 15 prospective cohort studies, were used in the final analysis. The risk of developing non-lung cancer was 1.09 (95% confidence interval (CI): 1.01–1.18, I² = 72.9%) per NO₂ increases of 10 µg/m³. There was also a significant association between exposure to PM_2.5 and PM₁₀ and the risk of non-lung cancer when the male and female populations were combined (pooled odds ratio/relative risk (OR/RR) = 1.22, 95% CI: 1.11–1.34; I² = 0.0% and pooled OR/RR = 1.26, 95% CI: 1.05–1.52; I² = 43.9%, respectively). Regarding the type of cancer, significant harmful effects of PM_2.5 were observed for liver cancer populations (pooled OR/RR = 1.21, 95% CI: 1.10–1.32; I² = 0.0%). Different types of cancer were positively associated with the incidence of non-lung cancer and PM₁₀ in the random-effect meta-regression analysis.

Long-term exposure to air pollutants appears to be associated with an increased risk of non-lung cancer. Care should be taken in interpretation, because the results for specific cancers were restricted.