Asbestosis as a precursor of asbestos related lung cancer: results of a prospective mortality study

Our plain-English summary of Asbestosis as a precursor of asbestos related lung cancer: results of a prospective mortality study, by J.M. Hughes, H. Weill (British Journal of Industrial Medicine, 1991).

The study

• Authors: J.M. Hughes, H. Weill
• Journal: British Journal of Industrial Medicine
• Published: 1991;48(4):229-33
• Cited by: 103 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. 004108).

Abstract

A prospective mortality study of 839 men employed in the manufacture of asbestos cement products in 1969 examined lung cancer risk in relation to lung fibrosis seen on chest x ray film, controlling for age, smoking, and exposure to asbestos. Twenty or more years after hire, no excess of lung cancer was found among workers without radiographically detectable lung fibrosis, even among long term workers (greater than or equal to 21.5 years); nor was there a trend in risk by level of cumulative exposure to asbestos among such workers. By contrast, employees with small opacities (greater than or equal to 1/0; ILO classification) experienced a significantly raised risk of lung cancer (nine observed deaths v 2.1 expected), even though their exposures to asbestos were similar to the exposures of long term workers without opacities. In this population, excess risk of lung cancer was restricted to workers with x ray film evidence of asbestosis, a finding consistent with the view that asbestos is a lung carcinogen because of its fibrogenicity.

In plain English

This prospective mortality study followed 839 men working in two New Orleans asbestos cement plants in 1969, when each had a chest x ray, through 1983. It compared their deaths 20 or more years after hire with Louisiana rates. Among 646 men with that much time since hire, respiratory cancer deaths were raised (26 observed v 15.4 expected). Long-term workers (employed 21.5 years or more) with no x ray abnormalities had six lung cancer deaths against 5.8 expected. Men with small opacities of profusion 1/0 or greater, the study's x ray evidence of asbestosis, had nine lung cancer deaths against 2.1 expected. This was a significant excess, although their asbestos exposures were similar to those of the long-term workers. Men without abnormalities showed no consistent lung cancer trend with cumulative exposure. After accounting for age, smoking and exposure, x ray category remained significant. Among ever smokers, the adjusted relative risk for men with such opacities was 2.88 compared with all others. The authors concluded the findings were consistent with asbestosis being a necessary precursor of asbestos induced lung cancer in this population, but said further supporting results were needed.

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: prospective mortality study, with comparison to expected deaths (standardised mortality ratios) and Cox survival analysis
• Who was studied: 839 men employed in 1969 at two New Orleans asbestos cement manufacturing plants who had chest x rays in 1969 and were followed through 1983. 646 of them were hired in 1963 or earlier and had at least 20 years since hire. Retirees and women were excluded.
• Exposure: Work in asbestos cement product manufacture. Cumulative asbestos exposure was estimated from job histories and hygiene data, in millions of particles per cubic foot of air times years (mppcf-y). The fiber types used were described in an earlier paper, not in this article.
• Main results:
  • Among the 646 workers 20 or more years after hire, cancer deaths were significantly raised (52 observed v 39.0 expected; p = 0.02), as were respiratory cancer deaths (26 v 15.4; p less than 0.01).
  • Long-term workers (employed 21.5 years or more) without x ray abnormalities had six lung cancer deaths against 5.8 expected.
  • Workers with small opacities of profusion 1/0 or greater (n = 77) had 9 lung cancer deaths against 2.1 expected (p less than 0.001, per the text). This was significantly different from the risk in long-term workers without abnormalities.
  • Workers with small opacities of profusion 0/1 (n = 83) had 4 lung cancer deaths v 2.3 expected. This was not a significant increase.
  • Among the 420 workers without x ray abnormalities, lung cancer showed no consistent trend across quintiles of cumulative asbestos exposure.
  • In survival analysis accounting for pack-years, age and asbestos exposure, x ray category was significant (one tailed p = 0.04). Among ever smokers, the adjusted relative risk for lung cancer in those with small opacities of 1/0 or greater, compared with all other groups combined, was 2.88.
  • Of 154 deaths during follow up, 29 were from lung cancer (all in cigarette smokers), six from asbestosis and eight from mesothelioma.
• The authors' conclusion: The authors concluded that the findings are consistent with lung fibrosis (asbestosis) having been a necessary precursor for asbestos induced lung cancer in this population. They said further supporting results are needed before a firm conclusion about such a mechanism can be reached.
• Limitations the authors state:
  • Expected deaths were based on Louisiana rates, while lung cancer rates in the local parishes were higher, so the calculated SMRs are likely somewhat inflated.
  • In this subset, lung cancer risk was not significantly associated with duration of employment or cumulative exposure. The authors suggest this may be due to the restricted range of these variables.
  • The authors state that further supporting results are needed before a firm conclusion on the mechanism can be reached.

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, Asbestos-Cement, Fibrosis, Cumulative Exposure, ILO Classification.

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