Occupational exposure to diesel motor exhaust and risk of lung cancer by histological subtype: a population-based case-control study in Swedish men

Our plain-English summary of Occupational exposure to diesel motor exhaust and risk of lung cancer by histological subtype: a population-based case-control study in Swedish men, by A. Ilar, N. Plato, M. Lewné, et al (European Journal of Epidemiology, 2017).

The study

• Authors: A. Ilar, N. Plato, M. Lewné, G. Pershagen, P. Gustavsson
• Journal: European Journal of Epidemiology
• Published: 2017;32(8):711-719
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

We investigated occupational exposure to diesel motor exhaust (DME) and the risk of lung cancer by histological subtype among men, using elemental carbon (EC) as a marker of DME exposure. 993 cases and 2359 controls frequency-matched on age and year of study inclusion were analyzed by unconditional logistic regression in this Swedish case-control study. Work and smoking histories were collected by a questionnaire and telephone interviews. DME was assessed by a job-exposure matrix. We adjusted for age, year of study inclusion, smoking, occupational exposure to asbestos and combustion products (other than motor exhaust), residential exposure to radon and exposure to air pollution from road traffic. The OR for lung cancer for ever vs. never exposure to DME was 1.15 (95% CI 0.94-1.41). The risk was higher for squamous and large cell, anaplastic or mixed cell carcinoma than for alveolar cell cancer, adenocarcinoma and small cell carcinoma. The OR in the highest quartile of exposure duration (≥34 years) vs. never exposed was 1.66 (95% CI 1.08-2.56; p for trend over all quartiles: 0.027) for lung cancer overall, 1.73 (95% CI 1.00-3.00; p: 0.040) for squamous cell carcinoma and 2.89 (95% CI 1.37-6.11; p: 0.005) for the group of undifferentiated, large cell, anaplastic and mixed cell carcinomas. We found no convincing association between exposure intensity and lung cancer risk. Long-term DME exposure was associated with an increased risk of lung cancer, particularly to squamous cell carcinoma and the group of undifferentiated, large cell, anaplastic or mixed carcinomas.

In plain English

This Swedish study asked whether men's workplace exposure to diesel motor exhaust was linked to lung cancer, and to which types of lung cancer. It was a population-based case-control study of men aged 40 to 75 living in Stockholm County during 1985 to 1990. The analysis included 993 men with lung cancer and 2359 men without it. Diesel exposure was estimated from work histories with a job-exposure matrix, using elemental carbon as a marker. Results were adjusted for age, year of study inclusion, smoking, occupational asbestos exposure, other combustion products, residential radon and traffic air pollution. After adjustment, ever having been exposed was not statistically significantly linked to lung cancer (odds ratio 1.15, 95% CI 0.94 to 1.41). Compared with never-exposed men, men exposed for 34 years or more had an odds ratio of 1.66 (95% CI 1.08 to 2.56). Associations were stronger for squamous cell carcinoma and for undifferentiated, large cell, anaplastic or mixed carcinomas. No clear trend was seen with the intensity of exposure. The authors concluded that the number of years exposed seemed most strongly associated with risk. They noted that diagnoses were not validated in a standardized way and that exposure may have been misclassified.

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 (part of the Lung Cancer in Stockholm, LUCAS, study), analyzed by unconditional logistic regression
• Who was studied: Men aged 40 to 75 living in Stockholm County at any time during 1985 to 1990. 993 lung cancer cases and 2359 controls were analyzed, frequency-matched on age and year of study inclusion.
• Exposure: Occupational diesel motor exhaust, estimated with a job-exposure matrix giving average annual elemental carbon exposure intensity for 72 exposed occupations, per calendar year from 1947 to 1994. Occupational asbestos exposure was not the exposure studied; it was one of the factors adjusted for, as a binary variable split at the median among the exposed.
• Main results:
  • All lung cancer, ever versus never exposed to diesel exhaust: adjusted OR 1.15 (95% CI 0.94–1.41), based on 227 exposed cases and 430 exposed controls. The crude OR was 1.33 (95% CI 1.11–1.59).
  • Ever exposure by cancer type, adjusted: undifferentiated, large cell, anaplastic or mixed carcinoma OR 1.57 (95% CI 1.05–2.34). Squamous cell carcinoma OR 1.30 (95% CI 0.99–1.71), described by the authors as of borderline significance.
  • All lung cancer, men exposed for at least 34 years (the highest quartile of duration) versus never exposed: adjusted OR 1.66 (95% CI 1.08–2.56), based on 73 cases and 113 controls. P for trend across duration quartiles was 0.027.
  • Squamous cell carcinoma, at least 34 years of exposure versus never exposed: adjusted OR 1.73 (95% CI 1.00–3.00), p for trend 0.040.
  • Undifferentiated, large cell, anaplastic or mixed carcinoma, at least 34 years of exposure versus never exposed: adjusted OR 2.89 (95% CI 1.37–6.11), p for trend 0.005.
  • Duration of exposure, other cancer types: the trend for adenocarcinoma was less pronounced (p for trend 0.093), and there was no trend for small cell carcinoma (p for trend 0.508).
  • Highest annual exposure intensity: no evident exposure-response relation for lung cancer overall or for any of the four histological subtypes examined.
  • Cumulative exposure, all lung cancer, highest quartile: adjusted OR 1.49 (95% CI 1.04–2.14).
• The authors' conclusion: The authors concluded that the study showed an association between diesel exhaust exposure and lung cancer risk. The risk appeared more prominent for squamous cell carcinoma and undifferentiated, large cell, anaplastic or mixed carcinoma than for alveolar cell cancer, small cell carcinoma and adenocarcinoma. Number of years exposed was the measure seemingly most strongly associated with risk.
• Limitations the authors state:
  • There was no standardized validation of the tissue diagnoses, and many pathologists were involved, which may have caused misclassification of cancer type.
  • The undifferentiated, large cell, anaplastic or mixed carcinoma group could not be subdivided because of the cancer registry's classification system.
  • Estimating exposure with a generic job-exposure matrix for the general population likely caused exposure misclassification, which the authors say tends to weaken observed risks. Exposure intensity was more likely to be misclassified than work history.
  • Too few never smokers were available to analyze them separately: only 3% of cases and 30% of controls were never smokers.
  • The observed risks reflect diesel exposure conditions of 20 or more years ago, before recent advances in diesel fuel quality.

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, Histological Subtype, Case-Control Study, Carcinoma, Adenocarcinoma, Squamous Cell Carcinoma.

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