The additional risk of malignant mesothelioma in former workers and residents of Wittenoom with benign pleural disease or asbestosis

Our plain-English summary of The additional risk of malignant mesothelioma in former workers and residents of Wittenoom with benign pleural disease or asbestosis, by A. Reid, N. de Klerk, G. Ambrosini, et al (Occupational and Environmental Medicine, 2005).

The study

• Authors: A. Reid, N. de Klerk, G. Ambrosini, N. Olsen, S.C. Pang, A.W. Musk
• Journal: Occupational and Environmental Medicine
• Published: 2005;62(10):665-9
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Aims: To examine the hypothesis that people with benign pleural disease or asbestosis have an increased risk of malignant mesothelioma beyond that attributable to their degree of asbestos exposure.

Methods: Former workers and residents of the crocidolite mining and milling town of Wittenoom are participating in a cancer prevention programme (n = 1988). The first plain chest radiograph taken at the time of recruitment into the cancer prevention programme was read for evidence of benign pleural disease and asbestosis, using the UICC classification. Crocidolite exposure of former workers was derived from employment records and records of dust measurements performed during the operation of the asbestos mine and mill between 1943 and 1966. Based on fibre counts, exposure for former residents was determined using duration of residence and period of residence (before and after a new mill was commissioned in 1957) and interpolation from periodic hygienic measures undertaken from personal monitors between 1966 and 1992. Cox proportional hazards modelling was used to relate benign pleural disease, asbestosis, asbestos exposure, and mesothelioma.

Results: Between 1990 and 2002, there were 76 cases of mesothelioma (56 of the pleura and 20 of the peritoneum). Cases had more radiographic evidence of (all) benign pleural disease, pleural thickening, blunt/obliterated costophrenic angle, and asbestosis than non-cases. Adjusting for time since first exposure (log years), cumulative exposure (log f/ml-years), and age at the start of the programme, pleural thickening (OR = 3.1, 95% CI 1.2 to 7.6) and asbestosis (OR = 3.3, 95% CI 1.3 to 8.6) were associated with an increased risk of peritoneal mesothelioma. There was no increased risk for pleural mesothelioma.

Conclusion: The presence of benign pleural disease, in particular pleural thickening, and asbestosis appears to increase the risk of mesothelioma of the peritoneum, but not of the pleura beyond that attributable to indices of asbestos exposure in this cohort of subjects exposed to crocidolite.

In plain English

The authors followed 1988 former workers and residents of Wittenoom, a crocidolite (blue asbestos) mining and milling town in Western Australia, who were enrolled in a cancer prevention programme. Each person's first programme chest X-ray was read for benign pleural disease and asbestosis. Crocidolite exposure was estimated from dust measurements, employment records and residence history. Between 1990 and 2002, 76 developed malignant mesothelioma: 56 of the pleura and 20 of the peritoneum. After adjusting for age, time since first exposure and cumulative exposure, diffuse pleural thickening (OR 3.05, 95% CI 1.22 to 7.62) and asbestosis (OR 3.29, 95% CI 1.26 to 8.59) were linked to higher peritoneal mesothelioma risk. After adjustment, no benign pleural disease and not asbestosis were linked to increased pleural mesothelioma risk. When both conditions were in one model, the peritoneal associations were no longer statistically significant. The authors concluded that these conditions were associated with increased peritoneal, but not pleural, mesothelioma risk beyond that attributable to exposure. They noted that exposure may have been underestimated, especially among the heavily exposed, and that participants were more heavily exposed than former workers who declined to take part.

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: Cohort analysis of participants in a cancer prevention programme, using Cox proportional hazards modelling
• Who was studied: 1988 former workers and residents of Wittenoom, Western Australia, who joined a cancer prevention programme (testing beta carotene and retinol supplements) before 1997. Mesothelioma was followed through cancer registries to September 2002 (Western Australia) or September 2000 (other Australian residents).
• Exposure: Crocidolite from the Wittenoom mine and mill (1943 to 1966). For workers, cumulative exposure in fibre-years per ml was calculated from dust measurements and company employment records. Residents not working directly with asbestos were assigned 1.0 f/ml from 1943 to 1957 and 0.5 f/ml from 1958 to 1966, with lower interpolated levels down to 0.010 f/ml in 1992.
• Main results:
  • Between 1990 and 2002 there were 76 cases of malignant mesothelioma (69 male, 7 female): 56 pleural and 20 peritoneal.
  • Diffuse pleural thickening was seen on X-ray in 9 (45%) of the 20 peritoneal cases, 12 (21%) of the 56 pleural cases and 225 (12%) of the 1912 non-cases.
  • Asbestosis was seen in 10 (50%) of peritoneal cases, 8 (14%) of pleural cases and 223 (12%) of non-cases.
  • For diffuse pleural thickening and peritoneal mesothelioma, the risk estimate was OR 5.06 (95% CI 1.99 to 12.9) adjusted for age only, and OR 3.05 (95% CI 1.22 to 7.62) after also adjusting for exposure. For pleural mesothelioma, the exposure-adjusted figure was OR 1.11 (95% CI 0.56 to 2.20).
  • For asbestosis and peritoneal mesothelioma, the risk estimate was OR 6.67 (95% CI 2.65 to 16.8) adjusted for age only, and OR 3.29 (95% CI 1.26 to 8.59) after also adjusting for exposure. For pleural mesothelioma, the exposure-adjusted figure was OR 0.68 (95% CI 0.31 to 1.49).
  • After adjusting for exposure, none of the benign pleural diseases and not asbestosis was associated with an increased risk of pleural mesothelioma.
  • Adjusting for exposure attenuated the peritoneal mesothelioma risk linked to all benign pleural disease combined and to blunt or obliterated costophrenic angle.
  • When pleural thickening and asbestosis were included in the same model, their associations with peritoneal mesothelioma (OR 2.27, 95% CI 0.85 to 6.07; OR 2.49, 95% CI 0.90 to 6.91) remained high but were not statistically significant.
  • The slope of the dose-response relation did not differ between people with and without benign pleural disease, or between people with and without asbestosis.
  • Average cumulative exposure was 38 f/ml-years for peritoneal cases, 13 f/ml-years for pleural cases and 5 f/ml-years for non-cases.
• The authors' conclusion: The authors concluded that diffuse pleural thickening and asbestosis were associated with increased risks of peritoneal mesothelioma beyond the risk calculated from the degree of asbestos exposure. This increased risk was not seen for pleural mesothelioma.
• Limitations the authors state:
  • The Wittenoom exposure estimates have been criticised as underestimates, and the underestimation may have been greater in more heavily exposed people. The authors suggest this may explain why the conditions predicted peritoneal better than pleural mesothelioma.
  • Programme participants were younger and more heavily exposed than former workers who declined to take part, which may bias the exposure-response relation.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Wittenoom, Western Australia

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Lung cancer, Mesothelioma, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Wittenoom, Asbestos Exposure, Crocidolite, Chest X-Ray, UICC, Mesothelioma, Pleura.

Related studies

• Familial aggregation of malignant mesothelioma in former workers and residents of Wittenoom, Western Australia — N. de Klerk, H. Alfonso, et al. (2013)
• The natural history of asbestosis in former crocidolite workers of Wittenoom Gorge — W. Cookson, N. De Klerk, et al. (1986)
• Prediction of mesothelioma, lung cancer, and asbestosis in former Wittenoom asbestos workers — G. Berry (1991)
• The effect of asbestosis on lung cancer risk beyond the dose related effect of asbestos alone — A. Reid, N. de Klerk, et al. (2005)
• Risk and significance of chest radiograph and pulmonary function abnormalities in an elderly cohort of former nuclear weapons workers — M.A. Mikulski, P.G. Hartley, et al. (2011)
• Chest pain in asbestos-exposed individuals with benign pleural and parenchymal disease — S. Mukherjee, N. de Klerk, et al. (2000)

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