Is asbestos or asbestosis the cause of the increased risk of lung cancer in asbestos workers?

Our plain-English summary of Is asbestos or asbestosis the cause of the increased risk of lung cancer in asbestos workers?, by K. Browne (British Journal of Industrial Medicine, 1986).

The study

• Author: K. Browne
• Journal: British Journal of Industrial Medicine
• Published: 1986;43(3):145-9
• Type of article: Editorial, Review
• Cited by: 65 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000379).

Summary of the article

This editorial examined whether the excess lung cancer risk in asbestos workers is caused by asbestos itself or by asbestosis, the lung fibrosis it produces. The question was posed in the 1938 report of the Chief Inspector of Factories, which found lung cancer in 12 of 103 fatal asbestosis cases. The author reviewed evidence from pathology, animal experiments, in vitro studies, radiology and epidemiology. He noted reports that lung cancers in asbestos workers more often arose in the lower lobes and were more often adenocarcinomas. In one rat inhalation experiment, 6 tumours (3.8%) occurred in 157 rats without asbestosis, against 11 (25%) in 44 rats with the same exposure that developed asbestosis. A short-fibre amosite sample produced neither asbestosis nor excess tumours. In vitro evidence suggested that asbestos may act as a tumour promoter rather than a complete carcinogen. In Canadian chrysotile miners, the lung cancer SMR was 1.08 in men whose last radiograph was normal and 3.5 in those with abnormal radiographs. Using a numerical example, the author argued that errors in exposure estimates can make a threshold response appear linear. He cited several lower-exposure cohorts without raised lung cancer rates. He concluded that a threshold seemed probable and that asbestosis, rather than asbestos itself, probably prepares the soil for malignancy, but that a definitive answer was still awaited.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This 1986 editorial by K Browne was a review of published evidence, not a new study. The author examined pathology, animal experiments, laboratory cell studies, chest X-ray studies and worker mortality studies on whether asbestos itself, or asbestosis (asbestos-caused lung scarring), explains the extra lung cancer in asbestos workers. Among the evidence cited, a 1955 mortality study found 11 lung cancer deaths with asbestosis and none (0.8 expected) without it. In rat experiments by Wagner and colleagues, 6 of 157 rats without asbestosis (3.8%) and 11 of 44 rats with asbestosis (25%) developed tumours. The author noted that several lower-exposure worker groups, including friction materials, asbestos-cement, dockyard and shipyard workers, did not show raised lung cancer rates. A worked example showed how errors in exposure estimates can make a threshold look like a straight-line dose-response. The author concluded that a threshold seemed probable and that asbestosis, rather than asbestos itself, probably prepares the ground for cancer. The author also stated that epidemiology cannot establish this and that a definitive answer was still awaited.

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: Editorial reviewing published evidence (pathology, animal experiments, in vitro studies, radiology and epidemiology); no new data were collected
• Who was studied: No study population of its own; the author reviewed earlier published studies of asbestos workers, experimental animals and cell systems
• Exposure: Asbestos in general, with reviewed animal studies of chrysotile and of short-fibre amosite; occupational cumulative exposure expressed as f/ml years
• Main results:
  • Reviewed: the first mortality study of asbestos workers (1955) found 11 lung cancer deaths associated with asbestosis and none without asbestosis, where 0.8 were expected (printed as '0-8')
  • Reviewed: in rat inhalation experiments by Wagner et al with brief asbestos exposure, 6 tumours occurred in 157 rats without asbestosis (3.8%, no higher than controls) and 11 tumours in 44 rats with asbestosis (25%)
  • Reviewed: in rat inhalation experiments by Davis et al, a short-fibre amosite sample produced no asbestosis and no excess of tumours
  • Reviewed: in Liddell and McDonald's cohort of Canadian chrysotile miners with at least one chest radiograph taken at work, there were 118 lung cancer deaths, an excess of 52. The SMR was printed as '1 08' for the 49 men whose last radiograph was normal and as '3 5' for those with 'less than normal' radiographs; the decimal points appear to have been lost in scanning.
  • The author's own numerical illustration: if a true threshold existed at 25 f/ml years and exposures were misclassified, true disease rates of 0, 0, 20% and 20% across four exposure categories would appear as 0, 5%, 15% and 20%, making a threshold look linear
  • Reviewed: several cohorts with lower-dose occupational exposure showed no raised lung cancer rates, including a friction materials factory, asbestos-cement factories, and dockyard and shipyard workers
• The authors' conclusion: The authors concluded that there was strong prima facie evidence of a threshold before occupational asbestos exposure increases lung cancer risk, and that it seemed probable that asbestosis, rather than asbestos itself, prepares the ground for malignancy, while a definitive answer was still awaited
• Limitations the authors state:
  • The author stated that a causal relation between lung cancer and asbestosis cannot be established by epidemiological means
  • The author stated that interpreting dose-response at low cumulative exposures is complicated by higher mortality in short-term workers
  • The author noted that the case-control studies discussed were not matched for duration of employment
  • The author stated that epidemiology is probably too blunt an instrument to bring much further enlightenment

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Fibrosis, Pathology, Epidemiology, Adenocarcinoma, Amosite, Chrysotile.

Related studies

• Asbestosis: a marker for the increased risk of lung cancer among workers exposed to asbestos — W. Weiss (1999)
• Absence of radiographic asbestosis and the risk of lung cancer among asbestos-cement workers: Extended follow-up of a cohort — M.M. Finkelstein (2010)
• Increased risk of lung cancer in pesticide-exposed male agricultural workers — E. Barthel (1981)
• The additional risk of malignant mesothelioma in former workers and residents of Wittenoom with benign pleural disease or asbestosis — A. Reid, N. de Klerk, et al. (2005)
• Increased mortality in COPD among construction workers exposed to inorganic dust — I.A. Bergdahl, K. Torén, et al. (2004)
• Temporal Patterns of Exposure to Asbestos and Risk of Asbestosis: An Analysis of a Cohort of Asbestos Textile Workers — A. Farioli, F.S. Violante, et al. (2018)

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