A threshold for asbestos related lung cancer

Our plain-English summary of A threshold for asbestos related lung cancer, by K. Browne (British Journal of Industrial Medicine, 1986).

The study

• Author: K. Browne
• Journal: British Journal of Industrial Medicine
• Published: 1986;43(8):556-8
• Cited by: 30 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. 000380).

In plain English

This article was a review of earlier published studies, not a new study. The author asked whether there is a cumulative asbestos exposure level below which lung cancer risk is not raised (a "threshold"). The author drew on eight worker groups with individually estimated exposure: Quebec chrysotile mining and milling, and cement, textile and friction products plants. The author added one New Jersey insulation materials study that gave only length of exposure. In the Quebec study, lung cancer relative risk did not rise below 30 mpcf years. In a Louisiana cement study, excess respiratory cancer was reported only above 100 mpcf years. Not all data agreed: for the South Carolina and Pennsylvania textile death-rate figures, the author noted no evidence for a threshold. The author concluded that every group with adequate data gave some evidence of a threshold. Where exposure estimates were given, it appeared to lie in the range of 25 to 100 f/cc years. The author said this fits the idea that asbestos raises lung cancer risk only where asbestosis is already present, but does not prove the two risks are linked. The author noted that short-term workers complicate interpretation.

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: Review of previously published studies of asbestos workers (commentary-style article; no new data collected)
• Who was studied: Worker groups from earlier published studies. Eight industrial groups had individually estimated exposure: the seven listed by McDonald in 1984 plus one more recent study. The groups were chrysotile mining and milling in Quebec; cement, textile and friction products in New Jersey; cement products in Louisiana; textiles in South Carolina and Pennsylvania; friction products in the United Kingdom; friction products in Connecticut; and textiles in the United Kingdom. One further study gave duration only: insulation materials in New Jersey. The article also briefly mentions asbestos cement factory, dockyard and shipyard studies.
• Exposure: Cumulative occupational asbestos exposure, expressed in the reviewed studies as mpcf years, f/ml years or p/ml years (or as months worked for the New Jersey insulation study). Industries were chrysotile mining and milling, cement, textile, friction and insulation products.
• Main results:
  • Quebec chrysotile mining and milling study: no increase in lung cancer relative risk below 30 mpcf years. The study's authors estimated this at about 100 f/ml years.
  • Louisiana cement products study: both the SMR and a case-control comparison (each case matched with four controls) were said to show excess respiratory cancer only above 100 mpcf years.
  • South Carolina and Pennsylvania textile studies: the SMR figures, unlike the case-control relative risks in the same series, showed no evidence for a threshold.
  • United Kingdom friction products study: the overall SMR for lung cancer was 106, an increase that was not statistically significant. Nine deaths from mesothelioma were attributed to work at the factory, and there was a small number of clinical asbestosis cases (no deaths).
  • Connecticut friction products study: the dose-response pattern was described as confusing. Men in the lowest cumulative exposure category had the highest mortality regardless of how long they were employed.
  • New Jersey insulation materials study (duration only): the author noted that relative risk began to rise only after more than six months of exposure in this factory.
  • Several studies of asbestos cement factories, dockyard workers and shipyard workers found lung cancer rates that were not raised. In some of these, mesotheliomas, pleural changes and some asbestosis showed that exposure was not negligible.
  • Where exposure estimates were given, the author judged the threshold for increased lung cancer risk to be somewhere in the range of 25 to 100 f/cc years.
• The authors' conclusion: The author concluded that every worker group with adequate individual exposure data gave some evidence of a threshold below which lung cancer risk does not appear raised. The author stated that a lung cancer threshold at or above the asbestosis threshold does not prove the risks are linked. The author considered it consistent with the hypothesis that asbestos raises lung cancer risk only where asbestosis is already present.
• Limitations the authors state:
  • The author stated that low-level dose-response data are hard to interpret because they include a disproportionate number of short-term workers, who often have higher lung cancer rates. The author said this does not apply to studies showing no increase, or to case-control studies matched for duration of employment.
  • The New Jersey insulation study made no estimate of cumulative exposure and, as the author notes, has been much criticized.

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.

Related studies

• Asbestos-related pleural thickening: effect of threshold criteria on interpretation — R. Greene, C. Boggis, et al. (1984)
• Asbestos-related mesothelioma: evidence for a threshold in animals and humans — E.B. Ilgren, K. Browne (1991)
• Asbestos-related cancer risk in patients with asbestosis or pleural plaques — J. Ameille, P. Brochard, et al. (2011)
• Keynote address: potential of in vitro tests in asbestos-related problems — I.J. Selikoff, A.L. Frank (1983)
• The threshold length for fiber-induced acute pleural inflammation: shedding light on the early events in asbestos-induced mesothelioma — A. Schinwald, F.A. Murphy, et al. (2012)
• Corporate influence on threshold limit values — B.I. Castleman, G.E. Ziem (1988)

Browse more research in British Journal of Industrial Medicine, or return to medical research.