Relationship between lung asbestos fiber type and concentration and relative risk of mesothelioma. A case-control study

Our plain-English summary of Relationship between lung asbestos fiber type and concentration and relative risk of mesothelioma. A case-control study, by A.J. Rogers, J. Leigh, G. Berry, et al (Cancer, 1991).

The study

• Authors: A.J. Rogers, J. Leigh, G. Berry, D.A. Ferguson, H.B. Mulder, M. Ackad
• Journal: Cancer
• Published: 1991;67(7):1912-20
• Cited by: 81 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004107).

Abstract

Lung tissue from 221 definite and probable cases of malignant mesothelioma reported to the Australian Mesothelioma Surveillance Program from January 1980 through December 1985 and from an age-sex frequency matched control series of 359 postmortem cases were examined by light microscopic (LM) and analytical transmission electron microscopic (TEM) analysis and energy dispersive x-ray analysis (EDAX). Concentrations of total fibers (coated and uncoated) (LM), crocidolite, amosite, chrysotile, and unidentified amphibole (TEM) (fibers/g dry lung tissue) were measured. Fiber concentrations less than 10 microns in length and greater than or equal to 10 microns in length were separately quantified. By comparing cases (221) and controls (359 LM, 103 TEM), odds ratios for increasing fiber concentrations compared with less than 15,000 fibers/g (LM) and less than 200,000 fibers/g (TEM) (the respective detection limits) were calculated. Univariate analyses showed statistically significant dose-response relationships between odds ratio and fiber concentration for all fiber concentration measures. The relationship between log(odds ratio) and log(fiber concentration) was linear. Multiple logistic regression analysis showed that a model containing crocidolite greater than or equal to 10 microns, amosite less than 10 microns, and chrysotile less than 10 microns as explanatory variables best described the data. The odds ratios for a X10 increase in fiber concentration (fibers/micrograms) were as follows: crocidolite greater than or equal to 10 microns, 29.4 (95% confidence interval [CI], 3.6 to 241); chrysotile less than 10 microns, 15.7 (95% CI, 6.1 to 40); amosite less than 10 microns, 2.3 (95% CI, 1.0 to 5.3). An additive risk model gave similar results. In a subgroup of cases and controls with only chrysotile in the lungs, a significant trend in odds ratio with increasing fiber content was found.

In plain English

This case-control study compared asbestos fiber levels in lung tissue from 221 people with definite or probable malignant mesothelioma, reported to the Australian Mesothelioma Surveillance Program from 1980 through 1985, with lung tissue from 359 controls of similar age and sex. The estimated risk of mesothelioma rose with lung fiber content for every fiber measure. In the model that best described the data, each tenfold rise in concentration was associated with odds ratios of 29.4 (95% CI 3.6 to 241) for crocidolite fibers 10 micrometers or longer, 15.7 (6.1 to 40) for chrysotile fibers shorter than 10 micrometers, and 2.3 (1.0 to 5.3) for amosite fibers shorter than 10 micrometers. In a small group with only chrysotile in the lungs, risk showed a statistically significant rising trend with fiber content. The authors concluded that, for Australia as a whole, long crocidolite carried the greatest risk. They said chrysotile's risk alone was hard to assess because of almost universal mixed exposure and possible differential clearance. They noted that not all cases came to postmortem and that controls came from one hospital in New South Wales.

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: Unmatched case-control study, with cases and controls frequency matched for age and sex
• Who was studied: Cases were 221 definite or probable malignant mesothelioma cases reported to the Australian Mesothelioma Surveillance Program from January 1980 through December 1985. Controls were 359 postmortem cases frequency matched for age and sex.
• Exposure: Asbestos fiber concentration in dry lung tissue. Total coated and uncoated fibers were counted by light microscopy. Crocidolite, amosite, chrysotile and unidentified amphibole were counted by transmission electron microscopy. Fibers under 10 micrometers and 10 micrometers or longer were counted separately.
• Main results:
  • In the univariate analyses, the relative risk of mesothelioma (estimated by odds ratio) rose progressively with lung fiber content for every fiber measure.
  • The final regression model included three fiber measures: crocidolite 10 micrometers or longer, amosite under 10 micrometers, and chrysotile under 10 micrometers.
  • Odds ratios for a tenfold increase in fiber concentration were 29.4 (95% CI 3.6 to 241) for crocidolite 10 micrometers or longer, 15.7 (95% CI 6.1 to 40) for chrysotile under 10 micrometers, and 2.3 (95% CI 1.0 to 5.3) for amosite under 10 micrometers.
  • An additive risk model gave a similar picture, with crocidolite 10 micrometers or longer and chrysotile under 10 micrometers the most important.
  • In a small group of cases and controls with only chrysotile found in the lungs, there was a statistically significant trend (P less than 0.005) of rising relative risk with rising lung fiber content.
  • Of the 25 cases with no amphibole found in the lung, 11 had a history of mixed exposure and two had a definite history of exposure only to chrysotile. Ten had no ascertainable history of asbestos exposure.
  • Where only crocidolite was found in the lungs, 15 of 30 cases had at least 10 to the power 5.5 fibers/g of crocidolite. Four of 39 controls did.
  • Where only amosite was found in the lungs, six of 20 cases had at least 10 to the power 5.5 fibers/g. One of 36 controls did.
  • In the light microscope analysis, relative risk showed a very clear gradient with the lung content of coated fibers (asbestos bodies). The gradient was clearer still for fibers 10 micrometers or longer.
• The authors' conclusion: The authors concluded that, for Australia as a whole, the greatest risk of mesothelioma is associated with exposure to crocidolite 10 micrometers or longer. They attributed this very likely to the wide distribution of Wittenoom crocidolite throughout Australia.
• Limitations the authors state:
  • Not all mesothelioma cases came to postmortem.
  • Other selection factors, such as the likelihood of compensation for a relative, may have affected which cases came to postmortem.
  • Controls came from one referral hospital serving one state, New South Wales. The authors judged any resulting bias likely to be small.
  • The risk from chrysotile alone was difficult to assess because of almost universal mixed exposure and possible differential clearance.
  • Occupational histories of the controls were not available.
  • Lung fiber content at death may not reflect the dose that produced the mesothelioma.
  • The fiber measures were correlated with each other, which can make multiple regression results misleading.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Chrysotile, Crocidolite, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Relative Risk, Mesothelioma, Case-Control Study, Malignant Mesothelioma, Crocidolite, Amosite, Chrysotile, Amphibole Group.

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