Cancer incidence within a cohort occupationally exposed to asbestos: a study of dose--response relationships

Our plain-English summary of Cancer incidence within a cohort occupationally exposed to asbestos: a study of dose--response relationships, by B. Clin, F. Morlais, G. Launoy, et al (Occupational and Environmental Medicine, 2011).

The study

• Authors: B. Clin, F. Morlais, G. Launoy, A.V. Guizard, B. Dubois, V. Bouvier, N. Desoubeaux, M.F. Marquignon, C. Raffaelli, C. Paris, F. Galateau-Salle, L. Guittet, M. Letourneux
• Journal: Occupational and Environmental Medicine
• Published: 2011;68(11):832-6
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: The aim of our study was to analyse the dose-response relationship between occupational asbestos exposure and risk of cancer.

Methods: Our study was a retrospective morbidity study based on 2024 subjects occupationally exposed to asbestos, conducted over the period 1 January 1978 to 31 December 2004. Analysis of the dose-response relationship between occupational asbestos exposure, as a time-dependant variable, and risk of cancer was performed using a Cox model. In order to account for the effect of latency, we conducted the analysis with a lag of 10 years.

Results: 285 cases of cancers were observed in our cohort. The relative risk of pleuro-peritoneal mesothelioma, lung cancer and colorectal cancer associated with asbestos exposure, adjusted for age as a time-dependant variable and for sex, was correlated with exposure intensity (or average exposure level, AEL). The risk of cancer, whatever the anatomical site, did not increase with the duration of exposure to asbestos.

Conclusion: While confirming the established relationship between asbestos exposure and pleuropulmonary and peritoneal cancers, this study also suggests a causal relationship between asbestos exposure and colorectal cancer.

In plain English

This study followed 2024 people who had worked at least a year at an asbestos plant in southern Calvados, Normandy, France. The plant made textiles containing about 20% crocidolite and chrysotile-based friction materials. Cancer registries recorded 285 cancers in the group between 1978 and 2004. Each worker's exposure was estimated from the company's own dust measurements, with a 10-year lag. The risk of pleural and peritoneal mesothelioma, lung cancer and colorectal cancer rose with average exposure intensity (trend p values 0.03, 0.02 and 0.02). Compared with the lowest-intensity group, the highest-intensity group had relative risks of 3.99 for lung cancer (95% CI 1.15 to 13.86), 4.19 for mesothelioma (0.92 to 19.15) and 7.20 for colorectal cancer (0.91 to 56.70). Length of exposure was not significantly linked to any cancer. Workers exposed to both chrysotile and amphibole had a higher lung cancer risk than those exposed to chrysotile alone. The authors concluded that the study confirmed the known links with mesothelioma and lung cancer and suggested a dose-response relationship with colorectal cancer. They noted a small sample size and no individual data on smoking or alcohol.

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: Retrospective cohort (morbidity) study using cancer registry data, analysed with Cox models and exposure treated as time-dependent with a 10-year lag
• Who was studied: 2024 people (1604 men, 420 women) alive in 1978 who had worked at least 1 year at an asbestos reprocessing plant in southern Calvados (Normandy), France, followed 1978 to 2004. 107 people whose vital status was unknown were excluded from analysis.
• Exposure: Occupational asbestos exposure in the manufacture of asbestos textiles (about 20% crocidolite) and chrysotile-based friction materials (clutch mechanisms, brake pads). 65.22% were exposed to chrysotile only and 34.74% to chrysotile and amphibole. Exposure was measured as duration, cumulative exposure index (fibres/ml × years) and average exposure level (fibres/ml), from a company employment exposure matrix based on dust measurements made since 1959.
• Main results:
  • Across the 2024 cohort members, 285 cancers were diagnosed between 1978 and 2004.
  • Highest versus lowest average exposure level (both sexes, adjusted for age and sex): primary bronchopulmonary (lung) cancer relative risk 3.99 (95% CI 1.15 to 13.86), pleuro-peritoneal mesothelioma 4.19 (95% CI 0.92 to 19.15), colorectal cancer 7.20 (95% CI 0.91 to 56.70). Trend p values in Table 1 were 0.02, 0.03 and 0.02 respectively.
  • Duration of exposure was not associated with an increased risk of cancer at any site.
  • For pleuro-peritoneal mesothelioma and colorectal cancer, the relationship was significant when exposure was expressed as average exposure level but not as cumulative exposure index.
  • Mixed chrysotile and amphibole exposure, compared with chrysotile alone, was associated with a lung cancer hazard ratio of 2.11 (95% CI 1.12 to 3.97). For colorectal cancer, the hazard ratio for mixed exposure was 1.78 (95% CI 0.76 to 4.18, p for trend 0.18).
  • For ear, nose and throat cancer, bladder and kidney cancer, oesophageal cancer and female genital tract cancer, risk was not significantly correlated with asbestos exposure.
• The authors' conclusion: The authors concluded that the study confirms a dose-response relationship between asbestos exposure intensity and pleuro-peritoneal mesothelioma and bronchopulmonary cancer, and suggests one between exposure intensity and colorectal cancer. They called for further studies with greater statistical power.
• Limitations the authors state:
  • Small sample size, which limits statistical power.
  • No individual data on possible confounding factors such as tobacco and alcohol use, physical exercise, diet, sunshine or air pollution.
  • Possible selection bias (healthy worker effect), because subjects had to be alive in 1978. This could have led to underestimating cancer risk at the highest exposures.

Topics

Medical terms in this study, explained in our Lexicon: Dose-response relationship, Asbestos Exposure, Latency, Relative Risk, Peritoneal Mesothelioma, Lung Cancer, Colorectal Cancer.

Related studies

• Digestive cancers and occupational asbestos exposure: incidence study in a cohort of asbestos plant workers — M. Boulanger, F. Morlais, et al. (2015)
• Occupational asbestos exposure and digestive cancers - a cohort study — B. Clin, F. Morlais, et al. (2009)
• Sources of uncertainty in dose-response modeling of epidemiological data for cancer risk assessment — L. Stayner, A.J. Bailer, et al. (1999)
• Cancer incidence among Swedish pulp and paper mill workers: a cohort study of sulphate and sulphite mills — E. Andersson, H. Westberg, et al. (2013)
• Incidence of digestive cancers and occupational exposure to asbestos — S. de La Provôté, N. Desoubeaux, et al. (2002)
• Pleural plaques and asbestosis: dose- and time-response relationships based on HRCT data — C. Paris, S. Thierry, et al. (2009)

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