Epidemiology of malignant mesothelioma--an outline

Our plain-English summary of Epidemiology of malignant mesothelioma--an outline, by J.C. McDonald (The Annals of Occupational Hygiene, 2010).

The study

• Author: J.C. McDonald
• Journal: The Annals of Occupational Hygiene
• Published: 2010;54(8):851-7
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In the 1960s and 1970s, well designed case-referent studies put beyond doubt that exposure to airborne asbestos fibres was a cause of malignant mesothelioma. Some 35 cohort mortality studies in a large variety of industries during the 20-year period, 1974-1994, showed a wide range of outcomes, but in general that the risk was higher in exposures which included amphiboles rather than chrysotile alone. Real progress began, however, with discoveries along several lines: the link between pleural changes and mineralogy, the concept and importance of biopersistence, the developments in counting and typing mineral fibres in lung tissue, and data on amphibole mining in South Africa and Australia for comparison with that on chrysotile in Canada and Italy. This led to the recognition of the potential contamination in North America of chrysotile with tremolite. A survey in Canada in 1980-1988 and other surveys demonstrated that crocidolite, amosite, and tremolite could explain almost all cases of mesothelioma. Effective confirmation of this was finally achieved with data on vermiculite miners in Libby, Montana, in the years 1983-1999, where exposure was to tremolite-actinolite and/or other amphibole fibres alone.

In plain English

This was a single-author commentary outlining the history of research on asbestos and malignant mesothelioma. It reported no new study, reviewing earlier work, much by the author's own group. Eight case-control studies published in 1965 to 1975 gave relative risks from 2.3 to 7.0. In some 35 manufacturing and application cohorts, mesothelioma proportional mortality per thousand was 2.5 to 5.6 in chrysotile-only categories and 23.1 in both amphibole-only categories. The author found these difficult to interpret. Eight lung-fibre studies all showed a substantial increase in odds ratios for amphibole fibres and little or none for chrysotile. The author noted these findings apply only to the time of death and cannot exclude an earlier role for chrysotile. In Quebec, fibrous tremolite was described as probably responsible for most cases in the mining region. In 406 vermiculite miners and millers in Libby, Montana, 12 deaths were attributed to mesothelioma. The author wrote that crocidolite, amosite and tremolite could explain almost all cases. The author added that the Quebec tremolite evidence was not specific, but Libby gave a degree of specificity.

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: Commentary (narrative review of earlier epidemiological studies, mostly by the author's group); no new data
• Who was studied: No study population of its own. It reviewed eight early case-control studies, about 35 cohort studies from 1974 to 1994, geographical case-referent surveys in North America and the UK, eight lung-fibre case-referent studies, the Quebec chrysotile miners and millers cohort, and a Libby, Montana vermiculite cohort of 406 miners and millers.
• Exposure: Airborne asbestos: chrysotile and amphiboles (crocidolite, amosite, tremolite). It also covered vermiculite ore at Libby containing 4 to 6% tremolite, with airborne fibres described as probably a mixture of amphiboles.
• Main results:
  • Eight early case-control studies (1965 to 1975, 657 cases in total) gave relative risks of 2.3 to 7.0.
  • In the reviewed cohort studies, mesothelioma proportional mortality rates per thousand were 2.5, 3.3, 3.9 and 5.6 in the four chrysotile-only industry categories. They were 23.1 in both amphibole-only categories, and 14.8 to 60.2 in mixed-fibre categories.
  • In the North American pathologist survey (668 cases, 1960 to 1975), relative risks were 46.0 for insulation work, 6.1 for asbestos production and manufacture, and 4.4 for other heating trades.
  • In the UK survey of people born 1943 or later, crocidolite and amosite were estimated to account for 80 to 90% of cases, and tremolite fibres were rarely found.
  • Eight lung-fibre case-referent studies in six countries all showed a substantial increase in odds ratios for amphibole fibres and little or none for chrysotile.
  • In the Quebec cohort, a statistically significant odds ratio of 2.55 (90% CI 1.52 to 4.27) was found in relation to 20 years' work in mines near those identified as the cause of pleural calcification. Risk was strongly related to time worked in the central Thetford area (Area A).
  • In the Libby cohort of 406 miners and millers followed to the end of 1998, there were 44 lung cancer deaths (SMR 2.40), 51 non-malignant respiratory disease deaths (SMR 3.09) and 285 deaths from all causes (SMR 1.27). Twelve deaths were attributed to mesothelioma (PMR 4.21%).
  • The 12 Libby mesothelioma deaths had a latency of 22 to 47 years (median 35.5 years) and showed a limited relationship to estimated exposure.
• The authors' conclusion: The author wrote that surveys showed crocidolite, amosite and tremolite could explain almost all cases of mesothelioma. The author judged the Quebec case-referent evidence supportive of the tremolite hypothesis but not specific, and said Libby provided a degree of specificity.
• Limitations the authors state:
  • In the secondary-industry cohorts, exposures were not defined, so the findings are difficult to interpret.
  • Lung-fibre findings apply only to the time of death and cannot exclude a role for chrysotile earlier.
  • Differences in biopersistence offer a possible mechanism, but mechanisms do not necessarily imply causation.
  • It remains unknown whether the mixed amphibole fibres found at Libby had always been present.
  • The Quebec case-referent evidence for tremolite is not specific.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma, Talc and vermiculite, Tremolite.

Medical terms in this study, explained in our Lexicon: Epidemiology, Malignant Mesothelioma, Amphibole Group, Chrysotile, Mineralogy, biopersistence, Tremolite, Crocidolite.

Related studies

• The epidemiology of mesothelioma in historical context — J.C. McDonald, A.D. McDonald (1996)
• Health of vermiculite miners exposed to trace amounts of fibrous tremolite — J.C. McDonald, A.D. McDonald, et al. (1988)
• A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans — D.H. Garabrant, S.T. Pastula (2018)
• Risk assessment using exposure intensity: an application to vermiculite mining — P.M. Vacek, J.C. McDonald (1991)
• Health effects of tremolite. This official statement of the American Thoracic Society was adopted by the ATS Board of Directors, June 1990 — (1990)
• Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in Libby, Montana — J.C. McDonald, J. Harris, et al. (2004)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.