Occupational exposure to asbestos and lung cancer in men: evidence from a population-based case-control study in eight Canadian provinces

Our plain-English summary of Occupational exposure to asbestos and lung cancer in men: evidence from a population-based case-control study in eight Canadian provinces, by P.J. Villeneuve, M.É. Parent, S.A. Harris, et al (BMC Cancer, 2012).

The study

• Authors: P.J. Villeneuve, M.É. Parent, S.A. Harris, K.C. Johnson, Canadian Cancer Registries Epidemiology Research Group
• Journal: BMC Cancer
• Published: 2012;12:595
• Cited by: 38 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Asbestos is classified as a human carcinogen, and studies have consistently demonstrated that workplace exposure to it increases the risk of developing lung cancer. Few studies have evaluated risks in population-based settings where there is a greater variety in the types of occupations, and exposures.

Methods: This was a population based case-control study with 1,681 incident cases of lung cancer, and 2,053 controls recruited from 8 Canadian provinces between 1994 and 1997. Self-reported questionnaires were used to elicit a lifetime occupational history, including general tasks, and information for other risk factors. Occupational hygienists, who were blinded to case-control status, assigned asbestos exposures to each job on the basis of (i) concentration (low, medium, high), (ii) frequency (<5%, 5-30%, and >30% of the time in a normal work week), and (iii) reliability (possible, probable, definite). Logistic regression was used to estimate odds ratios (ORs) and their corresponding 95% confidence intervals (CI).

Results: Those occupationally exposed to (i) low, and (ii) medium or high concentrations of asbestos had ORs for lung cancer of 1.17 (95% CI=0.92 - 1.50) and 2.16 (95% CI=1.21-3.88), respectively, relative to those who were unexposed. Medium or high exposure to asbestos roughly doubled the risk for lung cancer across all three smoking pack-year categories. The joint relationship between smoking and asbestos was consistent with a multiplicative risk model.

Conclusions: Our findings provide further evidence that exposure to asbestos has contributed to an increased risk of lung cancer in Canadian workplaces, and suggests that nearly 3% of lung cancers among Canadian men are caused by occupational exposure to asbestos.

In plain English

This population-based case-control study compared 1,681 men with newly diagnosed lung cancer and 2,053 men without lung cancer, recruited from eight Canadian provinces between 1994 and 1997. Participants reported their lifetime job histories. Occupational hygienists, who did not know which men had cancer, rated the asbestos exposure in each job. Men ever exposed to asbestos at work had an odds ratio for lung cancer of 1.28 (95% CI 1.02 to 1.61) compared with unexposed men. The odds ratio was 1.17 (95% CI 0.92 to 1.50) for low exposure and 2.16 (95% CI 1.21 to 3.88) for medium or high exposure. How long men were exposed was not related to risk. Medium or high exposure roughly doubled the risk in each smoking category, a pattern the authors found consistent with a multiplicative relationship between asbestos and smoking. They estimated that 3.1% of lung cancers in Canadian men were due to workplace asbestos. The authors could not tell fiber types apart and said they could not conclusively attribute the increased risk to chrysotile. Only 39 cases and 24 controls had medium or high exposure.

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 using self-administered questionnaires and expert assessment of exposure
• Who was studied: 1,681 men with incident lung cancer (cases) and 2,053 male controls from 8 Canadian provinces (no Quebec subjects), questionnaires 1994 to 1997; men under 40 and those who had worked less than one year were excluded
• Exposure: Occupational asbestos exposure assigned job by job by occupational hygienists blinded to case-control status, rated by concentration (low, medium, high), frequency and reliability; 'possibly exposed' was treated as unexposed; medium and high were combined because of small numbers; fiber type could not be distinguished (exposed workers were believed to have been exposed to chrysotile)
• Main results:
  • Men ever exposed to asbestos (233 cases, 224 controls) had an odds ratio of 1.28 (95% CI 1.02, 1.61) relative to unexposed men
  • By highest concentration ever reached: low exposure OR 1.17 (95% CI 0.92 to 1.50); medium or high exposure OR 2.16 (95% CI 1.21 to 3.88), relative to unexposed
  • Duration of occupational asbestos exposure was not related to lung cancer risk
  • Medium or high asbestos exposure roughly doubled lung cancer risk within each of the three smoking pack-year categories
  • Men with at least 40 pack-years of smoking and medium or high asbestos exposure had an OR of 38.59 (95% CI 10.78 to 138.08), compared with men with no asbestos exposure and fewer than 10 pack-years
  • The synergy index was 2.10 and the multiplicativity index 0.99, which the authors took as supporting a multiplicative interaction between asbestos and smoking
  • Using the ever-exposed OR of 1.28 and an exposure prevalence of 11.3% among controls, the authors calculated a population attributable risk of 3.1% for lung cancer in Canadian men
• The authors' conclusion: The authors concluded that their findings provide further evidence that asbestos exposure has contributed to an increased risk of lung cancer in Canadian workplaces. Because of possible exposure to other fiber types and the small number of men with medium or high exposure, they said they could not conclusively attribute the increased risks to chrysotile.
• Limitations the authors state:
  • Only about 68% of eligible cases and 64% of eligible controls completed questionnaires, which could bias the estimates
  • Asbestos exposure could not be distinguished by fiber type
  • Few men were exposed to medium or high levels, which limited analysis of the joint effect with smoking and of lung cancer subtypes
  • Jobs held for less than one year were not recorded; if the resulting misclassification was non-differential, the risk estimates would be understated
  • Too few lung cancers among never smokers (34 cases) to evaluate asbestos risk separately in that group

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, Case-Control Study, Occupational History, Asbestos Exposure, Odds Ratio, confidence interval.

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