Diesel Exhaust Exposure and the Risk of Lung Cancer—A Review of the Epidemiological Evidence
Diesel exhaust (DE) emissions are composed of gases and a particulate phase containing thousands of chemicals. In June 2012, a working group of the International Agency for Research on Cancer concluded that there was sufficient evidence for the carcinogenicity of DE in humans. However, these findings appear to be based upon selected epidemiological studies with certain important methodological limitations, particularly in the assessment of confounding effects and the assessment of DE exposures. To critically evaluate the association between DE exposure and the risk of lung cancer, we conducted a systematic review of published epidemiological evidences.
METHODS:
To comprehensively identify original studies on the association between DE exposure and the risk of lung cancer, literature searches were performed in literature databases for the period between 1970 and 2013, including bibliographies and cross-referencing.
RESULTS:
In total, 42 cohort studies and 32 case-control studies were identified in which the association between DE exposures and lung cancer was examined. In general, previous studies suffer from a series of methodological limitations, including design, exposure assessment methods and statistical analysis used. A lack of objective exposure information appears to be the main problem in interpreting epidemiological evidence. To facilitate the interpretation and comparison of previous studies, a job-exposure matrix (JEM) of DE exposures was created based on around 4,000 historical industrial measurements. The values from the JEM were considered during interpretation and comparison of previous studies. Overall, neither cohort nor case-control studies indicate a clear exposure-response relationship between DE exposure and lung cancer.
CONCLUSIONS: Epidemiological studies published to date do not allow a valid quantification of the association between DE and lung cancer