Occupational respiratory cancer and exposure to asbestos: a case-control study in a cohort of workers in the electricity and gas industry

Our plain-English summary of Occupational respiratory cancer and exposure to asbestos: a case-control study in a cohort of workers in the electricity and gas industry, by E. Imbernon, M. Goldberg, S. Bonenfant, et al (American Journal of Industrial Medicine, 1995).

The study

• Authors: E. Imbernon, M. Goldberg, S. Bonenfant, A. Chevalier, P. Guénel, R. Vatré, J. Dehaye
• Journal: American Journal of Industrial Medicine
• Published: 1995;28(3):339-52
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Cancers of the pleura, lung, and larynx between 1978 and 1989 among active male workers of Electricité de France-Gaz de France were studied in association with asbestos exposure using a case-control design nested within the cohort of workers of the company. The cohort included about 1,400,000 person-years, corresponding to a mean of 117,000 men per year. Exposure to asbestos and to some potential occupational confounders selected among agents from groups I, IIa, and IIb of the International Agency for Research on Cancer was assessed by a job-exposure matrix specific to the company. During the observation period, 12 cases of pleural cancer, 310 cases of lung cancer, and 116 cases of larynx cancer were registered in the cancer register of the company social security department. Four controls per case, matched for year of birth, were randomly selected among the cohort. Conditional logistic regression was used to estimate the odds ratios. A first analysis was conducted in order to assess the validity of the job-exposure matrix by investigating already known relationships between asbestos exposure and asbestosis. For asbestosis, a strong exposure-response relation was found with an odds ratio (OR) of 57.4 [95% confidence interval (CI): 17.0-194.0] in the highest exposure group. There was an elevated risk of pleural cancer (OR, 4.8, CI, 1.2-19.8). For lung cancer, significant ORs of 2.0 (CI, 1.3-3.2) and 1.9 (CI, 1.2-3.0) were found among the two highest cumulative exposure groups; adjustement for confounders slightly decreased the ORs. Squamous cell neoplasm of the lung was associated with asbestos exposure. The association between larynx cancer and asbestos exposure showed a tendency towards a nonsignificant increase in ORs in the highest cumulative exposure categories; this tendency disappeared when adjusting for occupational confounders. This study showed that occupational exposure to asbestos could increase the risk of pleural and lung cancer in a sector in which exposure levels are not considered to be high compared with other industrial settings.

In plain English

This case-control study was nested within active male workers of Electricité de France-Gaz de France, 1978 to 1989. It compared 12 cases of cancer of the pleura, 310 of lung cancer and 116 of laryngeal cancer with controls matched on year of birth (four selected per case; 47, 1,225 and 457 analyzed). Asbestos exposure was estimated with a company job-exposure matrix. Against 114 compensated asbestosis cases and 337 controls, the matrix gave an odds ratio of 57.4 (95% CI 17.0 to 194.0) in the highest exposure group. Asbestos exposure was associated with pleural cancer (OR 4.8, CI 1.2 to 19.8). For lung cancer, odds ratios were 2.0 (1.3 to 3.2) and 1.9 (1.2 to 3.0) in the two highest cumulative exposure groups. After adjustment for other workplace exposures, only the second-highest group stayed significant (OR 1.9, 1.2 to 3.0); the highest was 1.4 (0.8 to 2.6). For laryngeal cancer, increases were not significant and disappeared after adjustment. The authors concluded asbestos could increase pleural and lung cancer risk where exposure is not considered high. They had no smoking or drinking data.

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: Case-control study nested within a cohort of company workers. Exposure was assessed with a job-exposure matrix (MATEX), and odds ratios were estimated by conditional logistic regression.
• Who was studied: Active male workers of Electricité de France-Gaz de France (EDF-GDF), France, 1978 to 1989 (about 1,400,000 person-years). Cases were 12 cancers of the pleura, 310 lung cancers and 116 laryngeal cancers from the company social security cancer register. Four controls per case, matched for year of birth, were selected. The analyses used 47, 1,225 and 457 controls respectively. Retired workers were excluded. A separate validation analysis compared 114 cases of asbestosis compensated between 1986 and 1992 with 337 controls.
• Exposure: Occupational asbestos exposure, estimated by a company job-exposure matrix as cumulative exposure (fiber-years). The tasks were:
• heat insulation and its removal
• laying and cutting of washers
• maintenance of vehicle brakes
• use of welding shields
• storage of asbestos sheets

The company had used amosite and crocidolite (amphiboles) for heat insulation. Chrysotile was used for joining pipes in heat generators and for insulation, and is also found in vehicle brake linings. The matrix did not distinguish fiber types. Other agents (cadmium, chlorinated solvents, cutting oils, coal tar, crystalline silica, creosote and others) were assessed as possible confounders.

• Main results:
  • Asbestosis validation analysis (114 cases, 337 controls): the overall odds ratio for asbestos exposure was 15.35 (CI 7.9, 29.9).
  • Asbestosis: in the highest cumulative exposure group (mean 55.4 fiber-years) the odds ratio was 57.4 (95% CI 17.0, 194.0 per Table II). The authors described a monotonic exposure-response relationship (trend test p less than 0.001).
  • Cancer of the pleura: 7 of 12 cases and 11 of 47 controls were exposed to asbestos. The odds ratio was 4.8 (CI 1.2, 19.8), which the authors reported remained significant after adjusting for socioeconomic status (SES-adjusted OR 4.7, CI 1.0, 22.0 in Table III).
  • Cancer of the pleura, analysis restricted to cases with at least 20 years of exposure and their matched controls: SES-adjusted odds ratio 7.1 (CI 1.0, 50.1).
  • Lung cancer, workers ever exposed to asbestos compared with never exposed: SES-adjusted odds ratio 1.4 (95% CI 1.0, 1.8), described as significant.
  • Lung cancer by cumulative exposure: SES-adjusted odds ratios were 2.0 (CI 1.3, 3.2) and 1.9 (CI 1.2, 3.0) in the two highest exposure categories (mean 8.1 and 34.2 fiber-years).
  • Lung cancer, further adjusted for cadmium, chlorinated solvents, cutting oils, creosote, coal tar and crystalline silica: the exposure-response pattern was irregular. The association remained significant in the third exposure category (OR 1.9, 95% CI 1.2, 3.0). The highest category had OR 1.4 (0.8, 2.6) in Table VI, which was not statistically significant.
  • Lung cancer, ignoring exposure in the 20 years before diagnosis: the odds ratio in the highest category was 1.6 (CI 0.98, 2.7).
  • Lung cancer by cell type: asbestos exposure was significantly associated with squamous cell carcinoma (OR 1.8, 95% CI 1.1, 2.96). Odds ratios for other cell types were not significant.
  • Squamous cell lung carcinoma: odds ratios were 2.7 and 2.4 in the two highest asbestos exposure categories. No such increase was found for other lung cancer types.
  • Laryngeal cancer, ever exposed to asbestos compared with never exposed: odds ratio 1.5 (95% CI 0.9, 2.4), described as almost significant.
  • Laryngeal cancer by cumulative exposure: odds ratios tended to rise in the two highest categories (2.1 and 1.6), but these were not significant.
  • Laryngeal cancer: the rising tendency disappeared after adjustment for other occupational factors.
• The authors' conclusion: The authors concluded that occupational asbestos exposure could increase the risk of pleural and lung cancer in a sector where exposure levels are not considered high compared with other industrial settings. They found an effect at lower cumulative exposure levels than in earlier positive studies. For laryngeal cancer, they said the findings suggest a possible role of asbestos, but the effect disappeared on adjustment. They said the cell-type findings need further confirmation.
• Limitations the authors state:
  • There were no data on the smoking and drinking habits of the subjects.
  • Cancers occurring after workers left the company (retirees) could not be included. The authors said long-term effects were probably underestimated.
  • The small number of pleural cancer cases made an exposure-response analysis impossible.
  • The job-exposure matrix produces nondifferential misclassification and did not distinguish fiber types. The authors said both features would tend to underestimate risk.
  • Some subjects may have been exposed to asbestos before joining the company and been wrongly classified as unexposed by the matrix.
  • For laryngeal cancer, the occupational exposures were closely correlated, which limited more precise analysis.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Power plants and utilities.

Medical terms in this study, explained in our Lexicon: Case-Control Study, Pleura, Asbestos Exposure, Lung Cancer, Laryngeal Cancer, Odds Ratio, confidence interval, Cumulative Exposure.

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