Occupational exposure to diesel and gasoline emissions and lung cancer in Canadian men

Our plain-English summary of Occupational exposure to diesel and gasoline emissions and lung cancer in Canadian men, by P.J. Villeneuve, M.É. Parent, V. Sahni, et al (Environmental Research, 2011).

The study

• Authors: P.J. Villeneuve, M.É. Parent, V. Sahni, K.C. Johnson, Canadian Cancer Registries Epidemiology Research Group
• Journal: Environmental Research
• Published: 2011;111(5):727-35
• Cited by: 41 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The International Agency for Research on Cancer classifies diesel exhaust as a probable human carcinogen; this decision is based largely from lung cancer evidence. Gasoline exhaust is classified as a possible carcinogen. Epidemiological studies are needed that improve upon some of the limitations of previous research with respect to the characterization of exposure, and the control for the potential confounding influence of smoking and other occupational exposures. Our objective was to investigate associations between occupational exposure to diesel and gasoline engine emissions and lung cancer. We used a case-control study design that involved men 40 years of age and older at the time of interview. Analyses are based on 1681 incident cases of lung cancer and 2,053 population controls. A self-reported questionnaire elicited a lifetime occupational history, including general tasks, and information on other potential risk factors. Occupational exposures to diesel and gasoline emissions, crystalline silica, and asbestos were assigned to each job held by study subjects by industrial hygienists who were blind to case-control status. Exposure metrics for diesel and gasoline emissions that were modeled included: ever exposure, cumulative exposure, and concentration of exposure. We found a dose-response relationship between cumulative occupational exposure to diesel engine emissions and lung cancer. This association was more pronounced for the squamous and large cell subtypes with adjusted odds ratios across the three increasing tertiles of cumulative lifetime exposure relative to those with no exposure of 0.99, 1.25, and 1.32 (p=0.04) for squamous cell carcinoma, and 1.06, 1.19, 1.68 (p=0.02) for large cell carcinoma. While the association with cumulative exposure to gasoline was weakly positive, it was not statistically significant. Our findings suggest that exposure to diesel engine emissions increases the risk of lung cancer particularly for squamous and large cell carcinoma subtypes.

Crown Copyright © 2011. Published by Elsevier Inc. All rights reserved.

In plain English

This population-based Canadian case-control study compared 1681 men aged 40 and older newly diagnosed with lung cancer and 2053 population controls surveyed in 1994 to 1997. Blinded hygienists rated diesel and gasoline exhaust, asbestos and crystalline silica exposure in the 97.4% of jobs with enough information. Adjusted for smoking, asbestos, silica and other factors, men ever exposed to diesel had an odds ratio of 1.06 (95% CI 0.89 to 1.25) versus unexposed men, not statistically significant. Across rising thirds of lifetime diesel exposure, versus unexposed men, odds ratios (95% CIs) were 0.99 (0.73 to 1.36), 1.25 (0.93 to 1.68) and 1.32 (0.98 to 1.77) for squamous cell carcinoma and 1.06 (0.64 to 1.76), 1.19 (0.72 to 1.97) and 1.68 (1.03 to 2.74) for large cell carcinoma, with significant trends. Diesel showed no significant association with adenocarcinoma or small cell carcinoma; gasoline exhaust showed none overall. Ever asbestos exposure, versus none, had an age-adjusted lung cancer odds ratio of 1.24 (95% CI 1.09 to 1.43). The authors concluded their study provides evidence that diesel exhaust increases squamous and large cell lung cancer risk.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: population-based case-control study
• Who was studied: Men aged 40 and older who had worked at least a year: 1681 with newly diagnosed lung cancer and 2053 population controls, from eight Canadian provinces, with questionnaires returned 1994 to 1997
• Exposure: Occupational exposure to diesel and gasoline engine emissions, assigned job by job by hygienists blind to case-control status. Of 15,646 reported jobs, 15,234 (97.4%) had enough information for exposure assessment. Asbestos and crystalline silica were also coded and used as adjustment variables (ever/never).
• Main results:
  • All lung cancers: men ever exposed to diesel, compared with men unexposed to diesel, had a fully adjusted odds ratio of 1.06 (95% CI 0.89 to 1.25). This was not statistically significant.
  • All lung cancers: across increasing tertiles of cumulative diesel exposure, compared with unexposed men, the fully adjusted odds ratios were 0.93, 1.03 and 1.12 (p for trend 0.07).
  • Squamous cell carcinoma: across increasing tertiles of cumulative diesel exposure, compared with unexposed men, the adjusted odds ratios were 0.99 (95% CI 0.73 to 1.36), 1.25 (0.93 to 1.68) and 1.32 (0.98 to 1.77), with p for trend 0.04. The highest tertile's interval includes 1.
  • Large cell carcinoma: across increasing tertiles of cumulative diesel exposure, compared with unexposed men, the adjusted odds ratios were 1.06 (95% CI 0.64 to 1.76), 1.19 (0.72 to 1.97) and 1.68 (1.03 to 2.74), with p for trend 0.02.
  • Diesel exposure showed no statistically significant associations with adenocarcinoma or small cell carcinoma.
  • Gasoline engine emissions showed no clear association with lung cancer. Fully adjusted odds ratios across cumulative tertiles were 0.92, 1.08 and 1.11 (p for trend 0.68), and none was statistically significant.
  • Asbestos: men ever occupationally exposed to asbestos (629 cases, 668 controls) had an age-adjusted lung cancer odds ratio of 1.24 (95% CI 1.09 to 1.43) compared with never-exposed men. This estimate was adjusted for age only. Crystalline silica gave 1.19 (95% CI 1.04 to 1.35).
  • Compared with office workers, odds ratios for all lung cancers were above 1 for 15 of the 17 job groups examined with known engine-exhaust exposure.
• The authors' conclusion: The authors concluded that the study provides evidence that diesel engine emissions increase the risk of squamous and large cell lung cancer. They found gasoline engine emissions unrelated to lung cancer, and considered their risk estimates likely to be understated.
• Limitations the authors state:
  • Participation was modest: 64.3% of eligible cases and 60.8% of eligible controls completed a questionnaire, which could bias results.
  • Some exposure misclassification inevitably occurred, and residual confounding may persist.
  • The expert exposure coding could not be directly validated among the study participants.
  • Only 34 lung cancer cases had never smoked, which limited the ability to examine risk by smoking status.
  • Non-occupational exposure to gasoline emissions could not be taken into account.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Lung Cancer, Confounding, Case-Control Study, Occupational History, Crystalline, Cumulative Exposure, Dose-response relationship.

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