Ambient particulate matter and lung cancer incidence and mortality: a meta-analysis of prospective studies

Background: Chronic exposure to ambient particulate matter (PM) has been suggested to be associated with an increased risk of lung cancer, but the results were inconsistent. We performed a systematic review and meta-analysis of prospective studies to assess the association between exposure to PM and the incidence and mortality of lung cancer in adults. Methods: We searched PUBMED and EMBASE databases for prospective cohort studies that evaluated the association between PM2.5 (diameter < 2.5 mu m), PM10 (diameter < 10 mu m) and lung cancer incidence and mortality. Relative risks (RRs) and 95% confidence interval (CI) were calculated using fixed-effect or random-effects models when appropriate. Results: We initially identified 1987 citations, and 19 prospective cohort studies were finally included in our meta-analysis. The pooled adjusted RRs for lung cancer mortality were 1.09 (95% CI: 1.06-1.11; I-2 = 18.3%, P = 0.26) for 10 mu g/m(3) increase in the concentration of PM2.5 (12 studies), and 1.05 (95% CI: 1.03-1.07; I-2 = 41.9%, P = 0.11) for 10 mg/m(3) increase in the concentration of PM10 (seven studies). The increased risk of lung cancer mortality associated with PM2.5 and PM10 was consistent across most subgroups. PM10 (three studies) and PM2.5 (two studies) were not found to be significantly associated with lung cancer incidence. Conclusions: Ambient PM2.5 and PM10 pollutions are prospectively associated with a significantly increased risk of lung cancer mortality. More studies addressing the association between PM and lung cancer incidence are required.