Interaction between occupational exposure to diesel exhaust and tobacco smoking in determining lung cancer risk: A meta-analysis

Background While an association between exposure to diesel exhaust (DE) and risk of lung cancer has been reported in several studies, its interaction with tobacco smoking in determining lung cancer risk is not well characterized. This study aims at performing a systematic review and meta-analysis of results of epidemiology studies on this. Methods Studies included in the systematic review were identified from PubMed, Scopus, and Embase, without limitation of year of publication or language. Two reviewers independently reviewed the studies and abstracted relevant data from selected studies, applied a customized quality assessment tool and calculated the relative risks (RRs) and 95% confidence intervals (CIs) for the interaction between DE exposure and tobacco smoking on a multiplicative scale. Next, a random-effects meta-analysis of the interaction RR was conducted. Results Seven studies were included in the meta-analysis, of which two were cohort and five case-control studies. Results on the interaction were heterogeneous (I²=45.6%). The summary RR for interaction was 0.79 (95% CI, 0.42-1.46). There was no indication of publication bias. There was no increased risk of lung cancer among non-smoking workers exposed to DE. Conclusions This meta-analysis suggested a less-than-multiplicative effect between DE exposure and tobacco smoking in determining lung cancer risk, but the hypothesis of multiplicative interaction cannot be rejected. The small number of relevant studies and the high heterogeneity among them prevent from definite conclusions.