Occupational risk factors for brain cancer in Canada

Our plain-English summary of Occupational risk factors for brain cancer in Canada, by S.Y. Pan, A.M. Ugnat, Y. Mao, et al (Journal of Occupational and Environmental Medicine, 2005).

The study

• Authors: S.Y. Pan, A.M. Ugnat, Y. Mao, Canadian Cancer Registries Epidemiology Research Group
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2005;47(7):704-17
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: We sought to examine the impact of occupational exposure on brain cancer risk.

Methods: Mailed questionnaires were used to collect information on lifetime employment history, occupational exposure to 18 chemicals, and other risk factors for 1009 incident cases of brain cancer and 5039 control subjects in Canada in 1994 to 1997.

Results: People exposed to asphalt and welding had respective odds ratio (and 95% confidence interval) of 1.29 (1.02-1.62) and 1.26 (0.98-1.45). An increased risk of brain cancer might be associated with exposure to asbestos, benzene, mineral or lubricating oil, isopropyl oil, and wood dust and with following occupations: teaching; protective service; metal processing and related jobs, and metal shaping and forming; knitting in textile processing; construction trades; and transport equipment operating.

Conclusions: Our study suggests a possible role for occupational exposure in the etiology of brain cancer.

In plain English

This was a population-based case-control study in eight Canadian provinces, part of the National Enhanced Cancer Surveillance System. It compared 1009 people with newly diagnosed, histologically confirmed brain cancer with population control subjects in 1994 to 1997; 5033 controls were analysed after six of 5039 were excluded for missing age. Participants answered mailed questionnaires about their lifetime jobs and whether they had worked for more than 1 year with any of 18 chemicals, including asbestos. The article does not name asbestos fiber types. For asbestos, 80 cases and 353 controls reported exposure. The odds ratio was 1.31 (95% confidence interval 1.01–1.69) adjusted for age and province. After adjusting for more factors it was 1.23 (0.95–1.59), which was not statistically significant. Fully adjusted results by years of asbestos exposure were also not statistically significant. For asphalt, the fully adjusted odds ratio was 1.29 (1.02–1.62). The authors concluded that brain cancer was possibly associated with asbestos and several other exposures and occupations, and that chance could not be ruled out. They noted possible recall bias, self-reported exposure, and multiple comparisons.

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 mailed questionnaires, analysed with unconditional logistic regression
• Who was studied: 1009 incident, histologically confirmed brain cancer cases (benign tumors including meningiomas excluded) and population control subjects aged 20 to 76 in eight Canadian provinces, 1994 to 1997. 5039 controls returned questionnaires and six were excluded for missing age, leaving 5033 controls in the analysis.
• Exposure: Self-reported work for more than 1 year with any of 18 chemicals (asbestos, arsenic salts, chromium salts, cadmium salts, asphalt, mineral or lubricating oil, benzidine, benzene, isopropyl oil, dyestuffs, vinyl chloride, pesticides, herbicides, mustard gas, radiation sources, welding, wood dust, others), plus years of exposure and lifetime occupations. No asbestos fiber type is specified.
• Main results:
  • Asbestos, both sexes (80 exposed cases, 353 exposed controls): odds ratio 1.31 (95% CI 1.01–1.69) adjusted for province and age, and 1.23 (0.95–1.59) after multivariable adjustment
  • Asbestos in men (72 cases, 311 controls): multivariable adjusted odds ratio 1.23 (0.92–1.61). Asbestos in women (8 cases, 42 controls): 1.16 (0.53–2.52)
  • Years of asbestos exposure, multivariable adjusted: '1 to 10 years' (54 cases, 186 controls) odds ratio 1.33 (0.96–1.84). Longer-duration category, printed as '10 years' with its cutoff symbol lost in the text (26 cases, 165 controls): 1.15 (0.85–1.80). P for trend 0.47. With adjustment for age and province only, the '1 to 10 years' category was 1.54 (1.12–2.12).
  • After full adjustment, most of the increased odds ratios for chemical exposures were no longer statistically significant
  • Both sexes, multivariable adjusted: asphalt odds ratio 1.29 (1.02–1.62); welding 1.26 (0.98–1.45)
  • For usual occupation, odds ratios were significantly increased for teaching, protective service, some metal processing and food processing jobs, knitting in textile processing, construction trades and transport equipment operating. Construction trades had an odds ratio of 1.34 (1.00–1.79) for usual occupation and 1.25 (1.01–1.55) for ever-held occupation.
• The authors' conclusion: The authors concluded that brain cancer risk was increased with asphalt and welding exposure, and possibly with asbestos, benzene, mineral or lubricating oil, isopropyl oil, wood dust and certain occupations. They said this supports a possible role for occupational exposure, but that chance cannot be ruled out and further investigation is needed.
• Limitations the authors state:
  • Possible recall bias, because brain cancer patients may better remember past chemical exposures
  • Chemical exposure was self-reported, which could cause misclassification of exposure
  • Some significant results may be due to chance from multiple comparisons
  • Small numbers in some occupations made some estimates unstable
  • People in some occupations had multiple exposures, making it hard to separate the effect of one hazard

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Odds Ratio, confidence interval, Etiology.

Related studies

• Mortality of brain tumors among asbestos insulation workers in the United States and Canada — H. Seidman, I.J. Selikoff, et al. (1982)
• The investigation of brain tumor occurrence in other occupational groups: introduction — I.J. Selikoff (1982)
• The INTEROCC case-control study: risk of meningioma and occupational exposure to selected combustion products, dusts and other chemical agents — D.M. McElvenny, M. van Tongeren, et al. (2018)
• A case-control study of occupational risk factors for laryngeal cancer — P. Wortley, T.L. Vaughan, et al. (1992)
• Identification of occupational cancer risks in British Columbia, Canada: a population-based case-control study of 1,155 cases of colon cancer — R. Fang, N. Le, et al. (2011)
• INTEROCC case-control study: lack of association between glioma tumors and occupational exposure to selected combustion products, dusts and other chemical agents — A. Lacourt, E. Cardis, et al. (2013)

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