The So-called Short-Fiber Controversy: Literature Review and Critical Analysis

Our plain-English summary of The So-called Short-Fiber Controversy: Literature Review and Critical Analysis, by V.L. Roggli (Archives of Pathology & Laboratory Medicine, 2015).

The study

• Author: V.L. Roggli
• Journal: Archives of Pathology & Laboratory Medicine
• Published: 2015;139(8):1052-7
• Type of article: Review
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Context: Numerous articles in the scientific literature indicate that pathogenic fibers with respect to asbestos-related diseases are those that exceed 5 μm in length. Nonetheless, some authors have expressed concerns regarding pathogenicity of shorter fibers.

Objective: To review the scientific evidence regarding pathogenicity (or lack thereof) of fibers less than or equal to 5 μm in length, with particular attention to publications indicating that such fibers might be hazardous.

Data Sources: The scientific literature was reviewed for experimental animal studies and human studies that address the role of fiber size in causation of disease. Sources included original studies, as well as review articles related to the topic.

Conclusions: Experimental animal studies involving inhalation of fibers have demonstrated that fibers greater than 5 μm in length are associated with both pulmonary fibrosis (ie, asbestosis) and malignancies (carcinoma of the lung and mesothelioma). There is no convincing evidence for a pathogenic effect for fibers that are 5 μm or less in length. Fiber analyses of human lung tissue samples provide further support for pathogenicity of long fibers, particularly the more biopersistent amphibole fibers. Similar observations have been reported for nonasbestos mineral fibers. Concerns expressed by some authors (eg, the greater abundance of short fibers) do not alter these conclusions. Similarly, in vitro studies demonstrating biological activity of short fibers do not override inhalational studies of whole animals or the epidemiological findings in humans.

In plain English

This article was a literature review in which the author examined published animal experiments, studies of human tissue, and review articles on whether asbestos fibers 5 micrometers or shorter cause disease. The author described animal inhalation studies in which fibers longer than 5 micrometers were associated with asbestosis, lung cancer and mesothelioma. The author also cited human lung tissue studies, including one of 78 mesothelioma cases that linked risk to amphibole fibers (amosite, crocidolite or tremolite) 8.0 micrometers or longer. The author then critiqued papers arguing that short fibers matter. Studies by Suzuki and colleagues reported mostly short chrysotile fibers in tissue from 64 mesothelioma cases. The author argued that these findings may reflect contamination and that the large number of short fibers in tissue does not show they cause disease. The author also argued that test-tube (in vitro) studies cannot override whole-animal inhalation studies and human epidemiology. The author concluded that animal and human tissue studies do not support a disease-causing role for fibers 5 micrometers or shorter.

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 literature review and critical analysis
• Who was studied: Published experimental animal studies, human studies (including lung tissue fiber analyses in mesothelioma cases) and review articles on fiber size and disease; no search method or date range was described
• Exposure: Asbestos fibers by length, especially fibers 5 micrometers or shorter compared with longer fibers. Fiber types discussed include chrysotile, amosite, crocidolite and tremolite, along with nonasbestos mineral fibers.
• Main results:
  • In the animal inhalation studies the author reviewed, fibers longer than 5 micrometers were associated with pulmonary fibrosis (asbestosis), carcinoma of the lung and mesothelioma.
  • The author cited Davis and colleagues: rats breathing an amosite preparation with extremely few fibers longer than 5 micrometers developed no tumors. Rats breathing amosite with considerable numbers of longer fibers had a clear excess of lung adenocarcinomas and pleural mesotheliomas.
  • The author cited McDonald and colleagues' lung fiber analyses of 78 mesothelioma cases. In that study, risk correlated with amphibole fibers (amosite, crocidolite or tremolite) 8.0 micrometers or longer.
  • The author cited a meta-analysis by Berman and Crump that found no convincing evidence that fibers shorter than 10 micrometers cause cancer.
  • Suzuki and colleagues reported mostly short chrysotile fibers in pleural tissue from 64 mesothelioma cases. The author judged those papers unreliable, citing possible contamination, improper controls, unconventional methods and faulty reasoning about causation.
  • The author noted that raw asbestos preparations consist of 80% to 95% fibers 5 micrometers or shorter, so the predominance of short fibers in tissue is not surprising.
  • The author stated that epidemiological studies of auto mechanics, who are exposed to brake dust made up mostly of very short fibers, have found no evidence of increased mesothelioma risk.
  • The author argued that in vitro studies cannot establish disease causation when animal models and human epidemiology do not support it.
• The authors' conclusion: The author concluded that studies in animal models and human tissue samples do not support a disease-causing role for fibers 5 micrometers or shorter. The author also concluded that the large number of such fibers in tissue and in vitro findings do not override inhalation studies and human epidemiology.

Topics

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

Medical terms in this study, explained in our Lexicon: Causation, Pulmonary Fibrosis, Carcinoma, Mesothelioma, Amphibole Group, Mineral Fiber.

Related studies

• A commentary on Roggli's "The So-Called Short-Fiber Controversy" — D. Egilman, T. Tran (2016)
• Biopersistence of rock wool in lungs after short-term inhalation in rats — Y. Kudo, Y. Aizawa (2008)
• Pulmonary fibrosis and ferruginous bodies associated with exposure to synthetic fibers — A.J. Ghio, W. Funkhouser, et al. (2006)
• Comparison of Calidria chrysotile asbestos to pure tremolite: inhalation biopersistence and histopathology following short-term exposure — D.M. Bernstein, J. Chevalier, et al. (2003)
• Models for mesothelioma incidence following exposure to fibers in terms of timing and duration of exposure and the biopersistence of the fibers — G. Berry (1999)
• Biological mechanisms of non-linear dose-response for respirable mineral fibers — L.A.T. Cox (2018)

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