Lung cancer and diesel exhaust: an updated critical review of the occupational epidemiology literature

Abstract

A recent review concluded that the evidence from epidemiology studies was indeterminate and that additional studies were required to support the diesel exhaust-lung cancer hypothesis. This updated review includes seven recent studies. Two population-based studies concluded that significant exposure-response (E-R) trends between cumulative diesel exhaust and lung cancer were unlikely to be entirely explained by bias or confounding. Those studies have quality data on life-style risk factors, but do not allow definitive conclusions because of inconsistent E-R trends, qualitative exposure estimates and exposure misclassification (insufficient latency based on job title), and selection bias from low participation rates. Non-definitive results are consistent with the larger body of population studies. An NCI/NIOSH cohort mortality and nested case-control study of non-metal miners have some surrogate-based quantitative diesel exposure estimates (including highest exposure measured as respirable elemental carbon (REC) in the workplace) and smoking histories. The authors concluded that diesel exhaust may cause lung cancer. Nonetheless, the results are non-definitive because the conclusions are based on E-R patterns where high exposures were deleted to achieve significant results, where a posteriori adjustments were made to augment results, and where inappropriate adjustments were made for the “negative confounding” effects of smoking even though current smoking was not associated with diesel exposure and therefore could not be a confounder. Three cohort studies of bus drivers and truck drivers are in effect air pollution studies without estimates of diesel exhaust exposure and so are not sufficient for assessing the lung cancer-diesel exhaust hypothesis. Results from all occupational cohort studies with quantitative estimates of exposure have limitations, including weak and inconsistent E-R associations that could be explained by bias, confounding or chance, exposure misclassification, and often inadequate latency. In sum, the weight of evidence is considered inadequate to confirm the diesel-lung cancer hypothesis.

Keywords::

• Cumulative exposure
• diesel exhaust
• elemental carbon
• epidemiology
• exposure-response
• latency
• lung cancer
• odds ratio

Acknowledgments

The authors gratefully acknowledge the critical and careful review provided by the anonymous reviewers. Their review comments stimulated our thinking on several critical issues and helped us improve the cogency of the arguments and evidence presented and the readability of the revised manuscript.

Declaration of interest

John Gamble helped prepare this review during the normal course of his work as an independent consultant with financial support from CONCAWE (CONservation of Clean Air and Water in Europe), a European trade association of oil companies working on environmental, health, and safety issues in refining and distribution. CONCAWE has nominated him as an industry observer for the IARC (International Agency for Research on Cancer) Monograph 105 Working Group Meeting June 5-12, 2012. The IARC Monograph is focused on diesel and gasoline engine exhaust. He also received financial support from CONCAWE for preparation of a previous review of diesel exhaust and lung cancer published in Critical Reviews in Toxicology in 2010. He retired from ExxonMobil Biomedical Sciences, Inc (EMBSI) in 2005.

Mark Nicolich is an independent consultant and helped prepare this review during the normal course of work with financial support from CONCAWE (CONservation of Clean Air and Water in Europe), a European trade association of oil companies working on environment, health, and safety issues in refining and distribution. He has not previously published any work concerning diesels engine exhaust. He was previously employed by ExxonMobil Biomedical Sciences, Inc (EMBSI).

Paolo Boffetta worked on this review as a consultant to the Mining Awareness Resource Group (MARG). He has been the principal investigator of several epidemiologic studies of diesel exhaust exposure and cancer. MARG is a coalition of mining companies and engine manufacturers and now includes FMC Wyoming, Tata Minerals, Morton Salt, Cargill Deicing, Mosaic Potash, Detroit Salt and Navistar. Two of the papers reviewed were prepared by scientists with the National Cancer Institute and the National Institute of Occupational Safety and Health and are the subject of litigation involving MARG (Case No. 11-30812, currently pending in the United State Court of Appeals for the Fifth Circuit).

This review was conducted independently by the authors and the interpretations and opinions offered are solely those of the authors and do not necessarily represent the views of CONCAWE, MARG or any other public or private clients of the authors.