Occupational exposure and lung cancer risk: a population-based case-referent study in Sweden

Our plain-English summary of Occupational exposure and lung cancer risk: a population-based case-referent study in Sweden, by P. Gustavsson, R. Jakobsson, F. Nyberg, et al (American Journal of Epidemiology, 2000).

The study

• Authors: P. Gustavsson, R. Jakobsson, F. Nyberg, G. Pershagen, L. Järup, P. Schéele
• Journal: American Journal of Epidemiology
• Published: 2000;152(1):32-40
• Cited by: 96 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This case-referent study investigated the lung cancer risk from occupational exposure to diesel exhaust, mixed motor exhaust, other combustion products, asbestos, metals, oil mist, and welding fumes. All cases of lung cancer in males aged 40-75 years among stable residents of Stockholm County, Sweden, were identified from 1985 to 1990. Referents were selected as a stratified (age, inclusion year) random sample. Information on lifetime occupational history, residency, and tobacco smoking was obtained from the study subjects or from next of kin. Response rates of 87% and 85% resulted in 1,042 cases and 2,364 referents, respectively. Occupational exposures were assessed by an occupational hygienist who coded the intensity and probability of each exposure. Risk estimates were adjusted for tobacco smoking, other occupational exposures, residential radon, and environmental exposure to traffic-related air pollution. For the highest quartile of cumulative exposure versus no exposure, the relative risk was 1.63 (95% confidence interval (CI): 1.14, 2.33) for diesel exhaust, 1.60 (95% CI: 1.09, 2.34) for combustion products, and 1.68 (95% CI: 1.15, 2.46) for asbestos. Dose-response analyses indicated an increase in lung cancer risk of 14% per fiber-year/ml for asbestos exposure. No increased risk was found for the other exposure factors. An overall attributable proportion of 9.5% (95% CI: 5.5, 13.9) was estimated for lung cancer related to diesel exhaust, other combustion products, and asbestos.

In plain English

This population-based case-referent study from Sweden examined whether seven workplace exposures, including asbestos, were linked to lung cancer in men. It compared 1,042 men aged 40 to 75 in Stockholm County diagnosed with lung cancer from 1985 to 1990 with 2,364 randomly selected men. Job histories came from questionnaires answered by the men or, for those who had died, by their next of kin. An occupational hygienist who did not know which men had cancer estimated their exposures. Results were adjusted for smoking, home radon, traffic air pollution and other workplace exposures. Men with the highest cumulative asbestos exposure (1.5 fiber-years/ml or more) had a relative risk of 1.68 (95% CI 1.15 to 2.46) compared with unexposed men. Risk rose about 14 percent per fiber-year/ml (relative risk 1.14, 95% CI 1.04 to 1.25). Lung cancer risk did not rise with the number of years of asbestos exposure. Diesel exhaust and other combustion products were also linked to higher risk. The other four exposures showed no consistent increase. The authors named possible errors in historical exposure estimates as the main weakness.

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-referent (case-control) study
• Who was studied: Men aged 40 to 75 who lived in Stockholm County, Sweden, at any time from 1985 to 1990 and had lived outside the county no more than 5 years during 1950 to 1990. There were 1,042 lung cancer cases (87% response rate) and 2,364 referents (85% response rate), drawn from a population referent group and a mortality-matched referent group. Information for deceased subjects came from next of kin.
• Exposure: Seven occupational exposures: diesel exhaust, mixed motor exhaust, other combustion products, asbestos, metals, oil mist and welding fumes. An occupational hygienist blinded to case status estimated the intensity and probability of exposure for each work period. Asbestos was measured in fibers/ml, and cumulative exposure was expressed in fiber-years/ml. The article does not name specific asbestos fiber types.
• Main results:
  • Men in the highest quartile of cumulative asbestos exposure (1.5 fiber-years/ml or more; 71 cases, 85 referents) had a relative risk of lung cancer of 1.68 (95% CI: 1.15, 2.46) compared with unexposed men. This estimate was adjusted for smoking, residential radon, environmental nitrogen dioxide, diesel exhaust and combustion products. Adjusting for combustion products attenuated the asbestos estimate, but it remained statistically significantly elevated.
  • In dose-response analysis, lung cancer risk rose with cumulative asbestos exposure: relative risk 1.14 (95% CI: 1.04, 1.25) per 1 fiber-year/ml. A model using continuous exposure gave 1.14 (95% CI: 1.06, 1.22).
  • Men whose highest asbestos exposure intensity, held for at least 1 year, was 0.3 fibers/ml or more (16 cases, 9 referents) had an adjusted relative risk of 5.20 (95% CI: 1.97, 13.74).
  • Lung cancer risk did not correlate with duration of asbestos exposure.
  • When all asbestos exposure probabilities were set to 1.0 to test for possible bias, the excess risk was still about 10 percent per fiber-year/ml.
  • The highest quartile of cumulative exposure was also associated with increased risk for diesel exhaust (1.63; 95% CI: 1.14, 2.33) and for combustion products (1.60; 95% CI: 1.09, 2.34). There was no consistent evidence of increased risk for mixed motor exhaust, metal dust, oil mist or welding fumes.
  • The estimated proportion of lung cancer cases in the population attributable to occupational asbestos exposure was 4.0 percent. For diesel exhaust, asbestos and combustion products combined it was 9.5 percent (95% CI: 5.5, 13.9).
• The authors' conclusion: The authors concluded that occupational asbestos exposure was associated with increased lung cancer risk, with a statistically significant dose-response trend of about 14 percent per fiber-year/ml. They noted that this was higher than the roughly 1 percent per fiber-year/ml indicated by earlier studies of highly exposed occupational cohorts. They also found increased risk for diesel exhaust and other combustion products.
• Limitations the authors state:
  • The authors considered error in exposure assessment, such as systematic over- or underestimation of historical exposure levels, the most significant methodological problem, possibly affecting the dose-response results. They said there was no way to evaluate this.
  • Multiplying intensity by probability of exposure could underestimate true asbestos exposure levels and thereby overestimate the risk per fiber-year/ml.
  • The risk estimates for diesel exhaust and combustion products were less precise because data on past exposure levels were sparse, and the authors said these estimates should be interpreted with caution.
  • Some matching strata were small, so the validity of the unconditional logistic regression model could be questioned. The authors reported that a conditional analysis for diesel exhaust gave very similar results.
  • Occupational histories came mainly from next of kin for cases (most of whom had died) and mainly from the subjects themselves for population referents. The authors included mortality-matched referents to evaluate this possible bias.

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, Occupational History, Environmental Exposure, Cumulative Exposure, Relative Risk, confidence interval, Dose-response relationship.

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