Neoplastic findings in experimental asbestos studies and conclusions for fiber carcinogenesis in humans

Our plain-English summary of Neoplastic findings in experimental asbestos studies and conclusions for fiber carcinogenesis in humans, by F. Pott (Annals of the New York Academy of Sciences, 1991).

The study

• Author: F. Pott
• Journal: Annals of the New York Academy of Sciences
• Published: 1991;643:205-18
• Type of article: Review
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

This paper gave a brief overview of animal carcinogenicity studies of asbestos, mainly inhalation experiments in rats, with some results from injection directly into the serous body cavities, and drew conclusions for fiber carcinogenesis in humans. In most chrysotile inhalation experiments, exposure for 35 hours per week for 12 months produced lung tumors in about 20 to 50% of animals. Calidria chrysotile induced no tumors. High tumor rates after crocidolite inhalation were reported in only one study, and the same group could not confirm them. Amosite and tremolite gave tumor rates of 32% and 51%. In data from Davis and colleagues on 'long' and 'short' chrysotile and amosite, no difference was detected between the two fiber types. The author stated that these data did not support the view that lung cancer is most closely associated with fibers longer than 10 µm, but could not disprove it. The rat dose-response differed by a factor of more than 100 from the estimated risk in chrysotile textile workers. About 5,000 µg of 'short' amosite per rat lung was not associated with any lung tumor, whereas about 5% of this mass of 'long' chrysotile was associated with a 55% tumor rate. The author proposed that fibers implanted in the bronchial wall cause lung cancer, which could explain the combined effect of asbestos and cigarette smoke. He concluded that inhalation tests can give false-negative results and that mineral fibers may need to be classified using studies in which fibers are placed directly into a serous cavity.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This article was the author's review of animal cancer experiments with asbestos, mostly inhalation studies in rats, plus some studies placing fibers directly into body cavities. In most chrysotile inhalation experiments reviewed, exposure for 35 hours per week for 12 months produced lung tumors in about 20 to 50% of rats. For crocidolite, high tumor rates were reported in only one inhalation study. Looking at data from Davis and colleagues, the author found no detectable difference between chrysotile and amosite. Rats with about 5,000 micrograms of "short" amosite in their lungs had no lung tumors, while about 5% of that mass of "long" chrysotile was associated with a 55% tumor rate. The author reported that rats needed exposure concentrations about one hundred times higher than humans (chrysotile textile workers, estimated from Doll and Peto) for a similar excess cancer rate. The author proposed, as a hypothesis, that fibers lodged in the bronchial wall drive lung cancer. The author concluded that inhalation tests can give false-negative results, so mineral fibers may need to be classified using injection into body cavities.

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: Review (brief overview) of published animal carcinogenicity studies, mainly inhalation experiments, with discussion of hypotheses on fiber carcinogenesis in humans
• Who was studied: Experimental animals in previously published studies, mainly rats (Table 2 also includes baboons and hamsters)
• Exposure: Inhaled chrysotile (including UICC A, UICC B, Calidria, and 'long' and 'short' samples), crocidolite, amosite and tremolite; also intraperitoneal injection of asbestos and man-made mineral fibers
• Main results:
  • In most reviewed chrysotile inhalation experiments in rats, exposure for 35 hours per week for 12 months gave a lung tumor incidence of about 20 to 50%
  • In one 1974 study by Wagner and colleagues, a 1-day exposure to UICC chrysotile A from Zimbabwe was followed by lung tumors in 11% of the animals
  • Calidria chrysotile did not induce tumors in experimental animals after inhalation or intraperitoneal injection
  • For crocidolite, high tumor rates were reported in only one inhalation study. Two later experiments by the same group each produced only one lung tumor and no mesothelioma
  • Davis and colleagues observed tumor rates of 32% after amosite and 51% after tremolite inhalation in rats, at higher fiber concentrations than in their crocidolite study
  • In the Davis data on 'long' and 'short' fibers, the author found no difference between the effect of chrysotile and amosite in rats
  • A rat lung burden of about 5,000 micrograms of 'short' amosite was not associated with any lung tumor, while about 5% of this mass of 'long' chrysotile was associated with a 55% tumor rate
  • Comparing rat data with human risk estimates for chrysotile textile workers, the author reported that rat exposure concentrations had to be about one hundred times higher than in humans for a similar excess cancer rate
  • In intraperitoneal tests in rats, a glass fiber type designed to disintegrate in the body (D/E) did not reach a carcinogenic result, while a durable type (G/F) proved carcinogenic
• The authors' conclusion: The author concluded that inhalation experiments can give false-negative results for fibers less potent than the crocidolite used, and that mineral fibers may have to be classified on the basis of studies in which fibers are administered directly into a serosal cavity
• Limitations the authors state:
  • Fiber numbers were not determined in all experiments, and precise counting of asbestos fibers, especially chrysotile, is very difficult
  • The rats were nonsmokers, while most asbestos workers may have been smokers, which may affect the rat-human comparison
  • There are no data on the number of fibers implanted in the bronchial wall, which the implantation hypothesis depends on
  • The author acknowledged that the earlier hypothesis on fiber size and carcinogenic potency may be wrong in some points

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Santa Rita mine, Joaquin Ridge near Coalinga, California

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Carcinogenesis, Chrysotile, Calidria, Crocidolite, Amosite, Tremolite, Lung Cancer, Dose-response relationship.

Related studies

• Review of animal/in vitro data on biological effects of man-made fibers — S.A. Ellouk, M.C. Jaurand (1994)
• Studies of carcinogenesis of asbestos fibers and their natural oils — J.S. Harington, F.J. Roe (1965)
• Human and experimental data on translocation of asbestos fibers through the respiratory system — J. Bignon, G. Monchaux, et al. (1979)
• Increased epidermal growth factor-receptor protein in a human mesothelial cell line in response to long asbestos fibers — J.C. Pache, Y.M. Janssen, et al. (1998)
• A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans — D.H. Garabrant, S.T. Pastula (2018)
• Long and short fiber amosite asbestos alters at a different extent the redox metabolism in human lung epithelial cells — C. Riganti, E. Aldieri, et al. (2003)

Browse more research in Annals of the New York Academy of Sciences, or return to medical research.