Mesothelioma in patients with nonoccupational asbestos exposure. An evidence-based approach to causation assessment

Our plain-English summary of Mesothelioma in patients with nonoccupational asbestos exposure. An evidence-based approach to causation assessment, by A.M. Marchevsky, P. Harber, L. Crawford, et al (Annals of Diagnostic Pathology, 2006).

The study

• Authors: A.M. Marchevsky, P. Harber, L. Crawford, M.R. Wick
• Journal: Annals of Diagnostic Pathology
• Published: 2006;10(4):241-50
• Type of article: Systematic review
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The specific parameters of nonoccupational asbestos exposures (NOAE) that can distinguish an idiopathic from an asbestos-caused malignant mesothelioma (MM) are controversial. A systematic literature review yielded 1028 cases with this putative association. Only 287 of those reports had a defined single exposure to a household, building occupant, or neighborhood/community asbestos source. The available "evidence" was used to develop semiarbitrary evidence-based causation guideline rules for the assessment of putative associations between MM and NOAE. The rules are classified into class A (tissue burden analysis shows asbestos body counts or fiber counts in lung tissues comparable to MM caused by occupational exposure to asbestos) and classes B to D based on whether certain combinations of NOAE features and MM (evidence) have been described in over 15% (class B), 5% to 15% (class C), and less than 5% (class D) of the patients reviewed. The proposed 4 classes of evidence-based causation guidelines provide a semiarbitrary framework to evaluate the causation of individual MM patients by NOAE based on decreasing levels of currently available evidence. The neoplasms in classes A to C patients are probably caused by NOAE, with decreasing weight of evidence in the 3 groups. There is minimal evidence to support the causation of MM by NOAE in class D patients. There is no evidence or only anecdotal evidence to support a causal association between MM and NOAE in individuals who cannot be classified into any of the 4 classes. Future studies are needed to provide more comprehensive data regarding the association between MM and NOAE.

In plain English

This was a systematic review. The authors searched English-language literature, in March 2004 and again in February 2006, for reports of mesothelioma linked to nonoccupational asbestos exposure. The 61 selected articles described 1028 cases, possibly including duplicates. The authors reported excluding 763 and analyzing 287, figures that do not add up. These were 150 household contacts of asbestos workers, 31 building occupants and 106 people exposed in their neighborhood or community. Considerably less than half of the articles reported fiber type, fiber burden, cell type or even sex, and data were too incomplete for meta-analysis. Among the neighborhood cases, about 70% appeared to be associated with crocidolite, and 2 of 106 involved chrysotile only. The authors proposed four classes. Class A requires lung tissue studies showing increased asbestos bodies or fibers comparable to occupationally caused mesothelioma. Classes B to D rest on arbitrary cutoffs for how often a combination of features was reported. The authors concluded that tumors in classes A to C are probably caused by nonoccupational exposure, with decreasing weight of evidence, and that class D has minimal supporting evidence.

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: Systematic literature review of English-language reports, used to propose semiarbitrary causation guidelines. Searches were done in March 2004, with a follow-up search in February 2006. A meta-analysis was attempted but was not possible.
• Who was studied: 61 published articles describing 1028 mesothelioma cases (which may include duplicates). Of these, 287 unique cases with a defined single exposure source were analyzed in detail: 150 household exposure, 31 building occupant exposure and 106 neighborhood/community exposure.
• Exposure: Nonoccupational asbestos exposure from three sources. Household (HOE): household contacts of asbestos workers, such as wives laundering work clothes. Building occupant (BOE): asbestos-containing materials in homes, schools and other public buildings. Neighborhood/community (NCE): living near an asbestos mine, mill, factory or similar source. Fiber type was unspecified in most household and building cases. Most neighborhood cases were associated with crocidolite.
• Main results:
  • Of the 1028 cases described in the 61 articles, 763 were reported as excluded from further analysis. Reasons included missing information on the exposure source, multiple exposure sources, or too few cases in an exposure group. 1028 minus 763 is 265, not the 287 cases the article says remained; the article does not explain the difference.
  • The 1028 cases may include duplicates; the detailed tables are based on unique cases.
  • Considerably less than 50% of the 61 articles reported asbestos fiber type, fiber burden analysis, histologic type, or even patient sex.
  • Tumor location was not specified in 60% of cases.
  • The histologic category of mesothelioma was not specified in 219 of the 287 analyzed cases.
  • The reports had too many missing data elements for a quantitative meta-analysis.
  • In the neighborhood/community group, about 70% of cases appeared to be associated with crocidolite exposure. Chrysotile-only exposure was reported in 2 of 106 of these patients.
  • Only 13 cases of peritoneal mesothelioma appeared among all the reviewed citations. Peritoneal mesothelioma with neighborhood/community exposure (2 of 106 cases) was placed in class D.
  • In the proposed scheme, class A covers patients whose lung tissue burden studies show increased levels of ferruginous bodies or asbestos fibers comparable to those in mesothelioma caused by occupational exposure.
  • Classes B, C and D apply when tissue burden studies are not available. They depend on whether a combination of exposure and tumor features was described in over 15%, 5% to 15%, or under 5% of the patients reviewed. One class B example is pleural mesothelioma with at least 2 years of household contact with an asbestos product manufacturing or shipyard worker.
  • The authors stated that there is no evidence, or only anecdotal evidence, for a causal association in individuals who cannot be placed in any of the 4 classes.
• The authors' conclusion: The authors concluded that mesotheliomas in class A to C patients are probably caused by nonoccupational asbestos exposure, with decreasing weight of evidence across the three classes, and that there is minimal evidence for causation in class D patients. They described the literature as limited and the scheme as a preliminary framework.
• Limitations the authors state:
  • The cutoffs used for classes B to D are arbitrary and do not take into account how common each exposure group is in the population, because that information was not available.
  • The authors acknowledged that the semiarbitrary criteria may not be the ideal way to form opinions on whether individual mesotheliomas were caused by nonoccupational exposure.
  • Probability statements of causation could not be developed, because most reviewed cases lacked control group information.
  • The guidelines contain no criteria for amphibole, chrysotile or mixed fiber exposure, because the reviewed cases did not provide enough data on fiber type.
  • Most reported cases came from small case series that often lacked control groups and details on exposure and fiber type.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Asbestos Exposure, Causation, Idiopathic, Malignant Mesothelioma, Systematic Review, Asbestos Body Formation, Occupational Exposure.

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