Some Aetiologic Considerations of Fiber Carcinogenesis

Our plain-English summary of Some Aetiologic Considerations of Fiber Carcinogenesis, by M.F. Stanton (1972).

The study

• Author: M.F. Stanton
• Published: Biological Effects of Asbestos Lyon, October 2-5. Paper 43A (1972)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This 1972 conference paper from the U.S. National Cancer Institute reported preliminary results of animal experiments still in progress. Different forms of crocidolite and chrysotile asbestos, fibrous glass, and aluminum oxide (fibrous whiskers and a non-fibrous form) were applied by surgery to the left pleura of female Osborne-Mendel rats at a single 40 mg dose. Each specimen was a separate experiment, apparently with 30 rats each. When these results were reported, the rats were still being observed over a planned 2-year period. The particles in each sample were sorted by length and diameter. Five samples were estimated to cause mesotheliomas in more than 50% of rats: the UICC reference crocidolite and chrysotile A, two very fine glass samples, and the aluminum oxide whiskers. Seven samples fell in a middle range. Five had caused no mesotheliomas so far, including fully pulverized crocidolite and chrysotile and non-fibrous aluminum oxide. The glass samples that were over 90% by weight fibers 2.5 microns or less in diameter were the most carcinogenic. The author concluded that the carcinogenicity of these materials was primarily related to structure rather than physicochemical properties. The author also noted that the tumor estimates were preliminary and that the fiber sizing was crude.

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: animal experiment (preliminary results of ongoing experiments; conference paper)
• Who was studied: female Osborne-Mendel rats, 11 to 14 weeks old, at the Laboratory of Pathology, National Cancer Institute, Bethesda, Maryland. Each test specimen was a separate experiment, and the methods give the group size as 30 rats, apparently per specimen. The rats were still being observed over a planned 2-year period after application when these preliminary results were reported.
• Exposure: various specimens of crocidolite and chrysotile (UICC reference samples, partly and fully pulverized samples, crude hand-stripped fibers), fibrous glasses of different sizes, aluminum oxide whiskers and non-fibrous aluminum oxide, each applied once at 40 mg on a 45 mg glass-fiber pledget to the left pleura by open thoracotomy
• Main results:
  • Five specimens gave an estimated mesothelioma incidence greater than 50%: the UICC standard reference samples of crocidolite and chrysotile A, two very fine fibrous glass samples with diameters of 3 microns or less, and the aluminum oxide whiskers
  • The aluminum oxide whiskers differ from asbestos and glass in internal structure and chemical composition, but their size distribution resembled that of UICC crocidolite
  • Seven samples of asbestos and glass fell in an intermediate (moderate to low) range of carcinogenicity
  • Five samples had not produced mesotheliomas so far: fully pulverized crocidolite, fully pulverized chrysotile, whole-fiber commercial glass, one separated AAA glass sample, and non-fibrous aluminum oxide
  • For crocidolite, none of the three samples at the extremes of fiber size gave as high an incidence as the UICC reference sample. Both progressive pulverization and keeping the sample in large fiber bundles reduced carcinogenicity
  • For chrysotile, particles smaller than 0.5 by 1.5 microns (as in fully pulverized chrysotile) decreased carcinogenicity, and fibers with diameters of more than 2.5 microns and lengths of more than 80 microns reduced carcinogenicity
  • For glass, samples composed over 90% by weight of fibers with diameters of 2.5 microns or less were the most carcinogenic, and carcinogenicity fell as more fibers exceeded this diameter
  • For glass, length did not seem critical: crude AAA fibrous glass applied virtually intact yielded more mesotheliomas than the same glass reduced to shorter lengths
• The authors' conclusion: The author concluded that the carcinogenicity of asbestos, glass and aluminum oxide is primarily related to structure rather than to physicochemical properties, and that small-diameter fibrous glass is a potent carcinogen in the rat pleura
• Limitations the authors state:
  • The experiments were still in progress and only preliminary results were available
  • Tumor incidence estimates were conservative and may need to be revised upwards
  • The analysis of fiber size distribution was crude and subject to considerable error
  • Tumor response could not be interpreted precisely because rats died at various times and from various causes
  • Apart from the whole-fiber commercial glass, the zero-incidence experiments had not progressed far enough to be sure no mesotheliomas would occur
  • Final conclusions on the sized glass fibers had to await more accurate tumor-incidence figures

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenesis, Crocidolite, Chrysotile, Pleura, Mesothelioma, UICC, Carcinogenic.

Browse return to medical research.