Lung cancer mortality and occupational exposure to asbestos among telephone linemen: a historical cohort study in France

Our plain-English summary of Lung cancer mortality and occupational exposure to asbestos among telephone linemen: a historical cohort study in France, by D. Meguellati-Hakkas, D. Cyr, I. Stücker, et al (Journal of Occupational and Environmental Medicine, 2006).

The study

• Authors: D. Meguellati-Hakkas, D. Cyr, I. Stücker, J. Févotte, C. Pilorget, D. Luce, P. Guénel
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2006;48(11):1166-72
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: The authors studied the mortality by lung cancer in telephone linemen exposed to asbestos at low levels during installation of telephone cables.

Methods: Three hundred eight lung cancers deaths were identified in the cohort. Exposure to asbestos and to other occupational carcinogens was assessed using a job-exposure matrix.

Results: The relative risk for lung cancer death associated with an estimated exposure of approximately 2 f/cc-years was 2.1 (95% confidence interval = 1.1-4.0) as compared with workers exposed to less than 0.5 f/cc-years. Mean annual exposure or exposure duration were not clearly related to lung cancer. Adjustment for other occupational lung carcinogens did not change this finding.

Conclusion: The observed mortality by lung cancer associated with asbestos exposure at low levels is higher than the prediction based on linear downward extrapolations from highly exposed occupational cohorts.

In plain English

This historical cohort study followed 34,305 men who worked as linemen at the French national telephone company from 1978 through 1996. Their asbestos exposure, mainly from cable installation in asbestos-insulated buildings, was estimated by experts with a job-exposure matrix, not measurements. The article does not say which fiber type the linemen were exposed to. Of 2989 deaths, 308 were from lung cancer, close to the number expected from national rates (SMR 0.94, 95% CI 0.84–1.05). Within the cohort, the top 5 percent by cumulative exposure (averaging 1.91 f/cc-years) had a relative risk of lung cancer death of 2.1 (95% CI 1.1–4.0) compared with men below 0.50 f/cc-years. Intermediate groups showed small, non-significant increases, with no linear dose-response. Adjusted for PAH, engine exhaust and arc welding fumes, the relative risk stayed at 2.1 but was no longer statistically significant (95% CI 0.9–5.3). Smoking data were not available. The authors concluded that lung cancer mortality at these low exposures may be higher than predictions from highly exposed cohorts. They suggested this might relate to peak exposures, an assumption they said requires confirmation.

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: Historical (retrospective) cohort study of mortality, with internal comparisons between exposure groups (Cox models) and comparison with French national rates (SMR)
• Who was studied: 34,305 men in the French national telephone utility who were employed as telephone linemen at any time. They were active in a technical branch on January 1, 1978, or hired between 1978 and 1994, and were followed from January 1, 1978 to December 31, 1996 (589,162 person-years).
• Exposure: Intermittent, low-level asbestos exposure. The article does not identify the fiber type for the linemen; chrysotile is named only in reference titles about other cohorts. Exposure came mainly from telephone cable installation and splicing in asbestos-insulated buildings and from using asbestos sheets as protection during welding. It was estimated with a job-exposure matrix built from expert, worker and questionnaire information. Mean annual exposure for exposed workers was estimated at 0.05 f/cc, and mean cumulative exposure at 0.87 f/cc-years for the whole cohort.
• Main results:
  • The whole cohort had 308 lung cancer deaths against 328.2 expected from French national rates, giving an SMR of 0.94 (95% confidence interval 0.84–1.05).
  • Men in the highest cumulative exposure category (above the 95th percentile, mean 1.91 f/cc-years, 16 lung cancer deaths) had a relative risk of 2.1 (95% CI 1.1–4.0). The comparison group was men with 0–0.50 f/cc-years (32 deaths). The result was statistically significant.
  • Intermediate cumulative exposure categories had relative risks of 1.2 to 1.4, none statistically significant, and there was no evidence of a linear dose-response relationship.
  • For mean annual exposure, workers above the 75th percentile had a non-significant relative risk of 1.3 (95% CI 0.9–1.8) compared with those below the 25th percentile. The authors said the exposure gradient was too small for a meaningful analysis.
  • Workers exposed more than 32.3 years had a relative risk of 1.6 (95% CI 0.9–3.0). None of the relative risks for exposure duration were statistically significant.
  • With a 5-year lag, the highest cumulative exposure group had a relative risk of 2.3 (95% CI 1.2–4.5). With a 20-year lag, the highest group had a relative risk of 1.4 (95% CI 0.7–2.8).
  • After adjustment for PAH, engine exhaust and arc welding fumes, the relative risk in the highest asbestos category was 2.1 (95% CI 0.9–5.3), no longer statistically significant. These other exposures showed no association with lung cancer death.
• The authors' conclusion: The authors concluded that lung cancer mortality in telephone linemen with low asbestos exposure may be higher than predicted from studies of highly exposed workers. Linear extrapolation would predict a relative risk of 1.02, against the 2.1 observed. They said the findings suggest a possible causal association and that the increase was possibly related to peak exposures, an assumption requiring confirmation.
• Limitations the authors state:
  • There were no individual data on tobacco smoking.
  • Past exposure measurements were very sparse or nonexistent in the company, so exposure was estimated by expert judgment.
  • Nondifferential exposure misclassification was likely.
  • Asbestos exposure in other companies or outside work was not known.
  • Peak exposures could not be observed directly because the study was retrospective.

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: Lung Cancer, Occupational Exposure, Cohort Study, Relative Risk, confidence interval, Asbestos Exposure.

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