Background incidence of mesothelioma: animal and human evidence

Our plain-English summary of Background incidence of mesothelioma: animal and human evidence, by E.B. Ilgren, J.C. Wagner (Regulatory Toxicology and Pharmacology, 1991).

The study

• Authors: E.B. Ilgren, J.C. Wagner
• Journal: Regulatory Toxicology and Pharmacology
• Published: 1991;13(2):133-49
• Type of article: Review
• Cited by: 26 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. 004418).

Abstract

Evidence is presented showing that mesotheliomas can have causes other than exposure to asbestos dust, in both experimental animals and humans. In experimental animals, for example, results from two major experimental laboratories suggest that at least 10% may be taken for background incidence, whereas a third laboratory suggests that the experimental group must have a rate exceeding 30% "Background" also includes mesotheliomas found in association with nonfibrous and fibrous nonasbestiform agents. Mesotheliomas in humans can be broadly classified in a manner similar to those of experimental animals: (1) spontaneously occurring, (2) those with a latent period less than 10 years, (3) childhood mesotheliomas, (4) familial cases, (5) cases before the 20th century, (6) mineralogically negative mesotheliomas, and (7) mesotheliomas caused by nonasbestiform agents. The importance of the acceptance of these "background" cases lies in the fact that a basis is provided for the study of the incidence of disease associated with various types of asbestos.

In plain English

This article was a review of published animal and human reports, not a new study. The authors argued that mesothelioma can occur without asbestos exposure, which they called a "background" incidence. In animals, they listed mesotheliomas found in at least eight species outside experiments, in untreated and sham-treated control rats, and after non-asbestos agents such as erionite, man-made fibers, metals, plastics, hormones, chemicals and viruses. Citing three laboratories, they reported that Wagner et al. regarded more than 10% in their rats as a cause for concern, Pott et al. reported control-group rates that may amount to 10%, and Stanton et al. counted a group as significantly above controls only if it exceeded 30%. For humans, they grouped cases into seven categories, including childhood, familial, pre-20th-century cases and cases with no asbestos found in lung tissue, as well as cases linked to erionite or radiation. The authors concluded that thresholds for different asbestos types, especially chrysotile, should be considered taking these background tumors into account.

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: Narrative review of published animal experiments and human case reports and series
• Who was studied: No new subjects. The review drew on published reports of mesothelioma in animals (at least eight species, many inbred rat strains, and experimental and control cohorts) and in humans (epidemiological series, case reports, and reviews of childhood, familial and other cases).
• Exposure: Agents other than asbestos. In animals: saline and other vehicles, sham operations, nonfibrous dusts, naturally occurring nonasbestiform fibers (e.g., palygorskite, erionite), synthetic fibers (ceramic, glass), metals, polymers, hormones, other chemicals and viruses. In humans: no elicitable exposure, erionite, man-made mineral fibers, chemicals, ionizing radiation and chronic inflammation.
• Main results:
  • In at least seven untreated inbred rat strains, the cited studies reported mesothelioma incidences of 0.3-0.8% in the pleura and 0.9-1.7% in the peritoneum.
  • Stanton et al. (1981), who used intrapleural implantation in rats, considered pleural sarcoma incidence in an experimental group significantly greater than in the combined control group only if it exceeded 30%.
  • Wagner et al. (1987), using intrapleural inoculation in their strain of F344 rats, regarded an incidence of more than 10% as a cause for concern.
  • Pott et al. (1987) reported that tumor rates in control groups of intraperitoneal studies may amount to 10%. The review authors suggested the background may be as high as 15-20% in certain intraperitoneal injection studies.
  • In human epidemiological series, the proportion of cases with no elicitable history of asbestos exposure ranged from 5% (McDonald and McDonald, 1980, for females) to 99% (Cochrane and Webster, 1978).
  • In the Fraire et al. (1988) review of childhood mesothelioma, slides were available for 22 of 80 identified cases. An expert panel accepted 10 as mesotheliomas, and "risk factors" were identified for 2 of the 10.
  • Marsh (1988) found four mesotheliomas among 16,661 man-made mineral fiber workers employed for 1 year or more in 17 U.S. plants. This was not considered statistically significant.
• The authors' conclusion: The authors concluded that the rarity of mesothelioma may reflect the protected position of the mesothelium rather than an inability to respond to other tumor-causing agents. They said that thresholds for the different types of asbestos, particularly chrysotile, should be considered taking into account tumors that occur spontaneously or are due to other agents.
• Limitations the authors state:
  • The authors noted that more data are needed on the role of substances other than asbestos.

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, Non-Asbestiform.

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