The effect of asbestosis on lung cancer risk beyond the dose related effect of asbestos alone

Our plain-English summary of The effect of asbestosis on lung cancer risk beyond the dose related effect of asbestos alone, by A. Reid, N. de Klerk, G.L. Ambrosini, et al (Occupational and Environmental Medicine, 2005).

The study

• Authors: A. Reid, N. de Klerk, G.L. Ambrosini, N. Olsen, S.C. Pang, G. Berry, A.W. Musk
• Journal: Occupational and Environmental Medicine
• Published: 2005;62(12):885-9
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Aims: To determine if the presence of asbestosis is a prerequisite for lung cancer in subjects with known exposure to blue asbestos (crocidolite).

Methods: Former workers and residents of Wittenoom with known amounts of asbestos exposure (duration, intensity, and time since first exposure), current chest x ray and smoking information, participating in a cancer prevention programme (n = 1988) were studied. The first plain chest radiograph taken at the time of recruitment into the cancer prevention programme was examined for radiographic evidence of asbestosis according to the UICC (ILO) classification. Cox proportional hazards modelling was used to relate asbestosis, asbestos exposure, and lung cancer.

Results: Between 1990 and 2002 there were 58 cases of lung cancer. Thirty six per cent of cases had radiographic evidence of asbestosis compared to 12% of study participants. Smoking status was the strongest predictor of lung cancer, with current smokers (OR = 26.5, 95% CI 3.5 to 198) having the greatest risk. Radiographic asbestosis (OR = 1.94, 95% CI 1.09 to 3.46) and asbestos exposure (OR = 1.21 per f/ml-year, 95% CI 1.02 to 1.42) were significantly associated with an increased risk of lung cancer. There was an increased risk of lung cancer with increasing exposure in those without asbestosis.

Conclusion: In this cohort of former workers and residents of Wittenoom, asbestosis is not a mandatory precursor for asbestos related lung cancer. These findings support the hypothesis that it is the asbestos fibres per se that cause lung cancer, which can develop with or without the presence of asbestosis.

In plain English

This study followed 1988 people from Wittenoom, Western Australia, exposed almost exclusively to crocidolite (blue asbestos). They were 1196 former miners and millers and 792 former residents who joined a vitamin A cancer prevention programme between 1990 and 1996. Each person's first programme chest x-ray was read for asbestosis; cumulative exposure was estimated and smoking recorded. Between 1990 and 2002, 58 developed lung cancer. Asbestosis appeared on x-rays of 21 of 58 cases (36%) and 220 of 1930 others (11%). After adjustment, current smokers had the highest risk (hazard ratio 26.5 versus never smokers, 95% confidence interval 3.54 to 198.5); only one never smoker developed lung cancer. Asbestosis (hazard ratio 1.94, 95% confidence interval 1.09 to 3.46) and higher cumulative exposure were each linked to higher risk. In people without asbestosis on x-ray, risk still rose with exposure. The exposure effect did not differ significantly with or without asbestosis. The authors concluded that asbestosis was not a necessary precursor for lung cancer here. They said the extra risk with asbestosis might reflect the fibrosis itself or underestimated exposure.

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 study of participants in a cancer prevention programme, followed for new lung cancers and analysed with Cox proportional hazards models
• Who was studied: 1988 people: 1196 former Wittenoom asbestos workers and 792 former Wittenoom residents, Western Australia, who joined a cancer prevention programme between 1990 and 1996. They were followed to September 2002 (Western Australian residents) or September 2000 (others).
• Exposure: Almost exclusively crocidolite from mining, milling and living in the town. Exposure was measured as estimated cumulative exposure in fibre-years per ml. Asbestosis was defined on the first chest x-ray by the UICC/ILO classification (profusion of small irregular opacities of 1/0 or more).
• Main results:
  • 58 incident lung cancers (52 in men, 6 in women) between 1990 and 2002
  • Radiographic asbestosis was present in 21 of 58 cases (36%), 220 of 1930 non-cases (11%), and 241 of 1988 participants overall (12%)
  • Adjusted hazard ratio for current smokers versus never smokers: 26.5 (95% CI 3.54 to 198.5)
  • Only 1 of the 58 lung cancer cases was a never smoker, compared with 532 never smokers among the 1930 non-cases
  • Adjusted hazard ratio for past smokers versus never smokers: 9.53 (95% CI 1.29 to 70.6)
  • Adjusted hazard ratio for radiographic asbestosis, all participants: 1.94 (95% CI 1.09 to 3.46)
  • Adjusted hazard ratio for cumulative asbestos exposure, all participants: 1.21 per log f/ml-y (95% CI 1.02 to 1.42)
  • The interaction between cumulative exposure and asbestosis was not significant (HR = 0.82, 95% CI 0.59 to 1.13, p = 0.23), so the exposure-response slope did not differ significantly between those with and without asbestosis
  • In participants without asbestosis at the start of the study, cumulative asbestos exposure was associated with increased lung cancer risk: HR 1.31 per log f/ml-y (95% CI 1.06 to 1.62)
  • 37 of the 58 lung cancer cases did not have radiographically defined asbestosis
• The authors' conclusion: The authors concluded that in this group asbestosis is not a necessary precursor for lung cancer, which supports the hypothesis that asbestos fibres themselves cause lung cancer. They said the extra risk with asbestosis may be due to the fibrosis itself or to underestimated asbestos exposure.
• Limitations the authors state:
  • The exposure estimates are possibly underestimates because few dust measurements were collected at Wittenoom
  • The extra risk seen with asbestosis may be due to underestimated exposure, with asbestosis acting as a marker of heavy exposure
  • There were too few people with asbestosis to analyse that group separately
  • Programme participants were younger and had higher exposure than people who were invited but did not join; the authors considered this would not unduly influence the within-group findings
  • Exposure data were of a different form for residents and workers, so the exposure assessment may differ between the two groups

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, Crocidolite, Lung cancer.

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

Related studies

• 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)
• Are children more vulnerable to mesothelioma than adults? A comparison of mesothelioma risk among children and adults exposed non-occupationally to blue asbestos at Wittenoom — A. Reid, P. Franklin, et al. (2018)
• The risk of lung cancer with increasing time since ceasing exposure to asbestos and quitting smoking — A. Reid, N.H. de Klerk, et al. (2006)
• No dose-dependent increase in fracture risk after long-term exposure to high doses of retinol or beta-carotene — G.L. Ambrosini, A.P. Bremner, et al. (2013)
• Age and sex differences in malignant mesothelioma after residential exposure to blue asbestos (crocidolite) — A. Reid, G. Berry, et al. (2007)
• Ultra-low-dose chest computer tomography screening of an asbestos-exposed population in Western Australia — F.J. Brims, C.P. Murray, et al. (2015)

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