The relationship between fibrosis and cancer in experimental animals exposed to asbestos and other fibers

Our plain-English summary of The relationship between fibrosis and cancer in experimental animals exposed to asbestos and other fibers, by J.M. Davis, H.A. Cowie (Environmental Health Perspectives, 1990).

The study

• Authors: J.M. Davis, H.A. Cowie
• Journal: Environmental Health Perspectives
• Published: 1990;88:305-9
• Type of article: Review
• Cited by: 40 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The association between occupational asbestos exposure and the development of both pulmonary fibrosis or asbestosis and pulmonary carcinomas is well documented. It has been suggested that the two pathological conditions are associated with asbestos-related carcinomas developing from areas of asbestosis and not occurring when exposure has been too low to produce this type of pulmonary scarring. Experimental inhalation studies so far published have not been designed to examine this association specifically, but many publications have reported that asbestos samples producing high levels of fibrosis is experimental animals are also very carcinogenic. Samples of asbestos or man-made fibers that produce little fibrosis also produce few tumors. These works are reviewed. In order to examine the association between fibrosis and tumor production in more detail, groups of animals with and without pulmonary tumors and with individual fibrosis measurements were assembled from a number of inhalation studies undertaken over a period of years at this Institute. It was found that animals with pulmonary tumors had almost double the amount of pulmonary fibrosis as animals of similar age that did not. In a few of the animals where tumors were found at an early stage of development, their origin from fibrotic areas could be confirmed, although in most cases where tumor deposits were widespread this was not possible. Experimental confirmation of the site of origin of most pulmonary tumors in asbestos-treated rats would require new studies with rats examined specifically at an age when early tumors would be expected.

In plain English

The authors reviewed published rat inhalation experiments and added a new analysis of rat data. They noted that asbestos samples causing high lung fibrosis (scarring) were often reported to be very carcinogenic, although no study had been designed to test the link directly. They then pooled records for 144 rats from 10 chrysotile and amosite inhalation studies at their Edinburgh institute. Of these rats, 85 had lung tumors (60 malignant, 25 benign) and 59 did not. Rats with tumors had fibrosis in 12.5% of the lung on average, against 7.3% in rats without, a statistically significant difference. Rats with benign tumors had more fibrosis (14.2%) than those with malignant ones (11.9%), a non-significant difference. Ten tumors occurred in rats with less than 4% fibrosis. Five of these were early tumors, all showing strong evidence of starting in the center of fibrotic areas. The authors concluded that their data supported the suggestion that these rats' lung tumors usually develop from areas of adenomatoid change alongside advanced fibrosis, and that specifically designed studies were needed to examine this further.

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 of published rat inhalation studies, plus a pooled analysis (analysis of variance) of individual-rat data from the authors' own earlier inhalation experiments
• Who was studied: 144 rats from 10 inhalation studies at the Institute of Occupational Medicine, Edinburgh: 85 with lung tumors (60 malignant, 25 benign) and 59 without
• Exposure: Inhaled chrysotile and amosite asbestos
• Main results:
  • In the review, the authors noted that many publications reported that asbestos samples producing high fibrosis in animals were also very carcinogenic (this is a finding of other studies)
  • Across all 144 rats, fibrosis occupied 12.5% of the lung in rats with tumors versus 7.3% in rats without tumors (p less than 0.001)
  • In 8 of the 10 individual experiments, rats with tumors had more fibrosis, but these within-experiment differences were not significant
  • The 25 rats with benign tumors had more fibrosis (14.2%) than rats with malignant tumors (11.9%); the difference was not significant
  • Of the 85 tumors, 10 occurred in rats with less than 4% of lung area occupied by advanced asbestotic lesions
  • Of those 10, five were early tumors that all showed strong evidence of originating in the center of areas of interstitial fibrosis or adenomatosis; the other five were advanced tumors confined to a single lung lobe
• The authors' conclusion: The authors concluded that the accumulated data support the suggestion that lung tumors in these rats usually develop from areas of adenomatoid change occurring along with advanced fibrosis, and that closer study would need specifically designed experiments
• Limitations the authors state:
  • Most tumors were found at an advanced stage, so their exact relationship with fibrotic lesions was often impossible to determine
  • The authors considered that their figures probably underestimate the difference in fibrosis between rats with and without tumors, because of the measurement techniques used and because only animals of advanced age were examined in detail
  • A growing malignant tumor could destroy the fibrotic area it arose from, lowering the recorded fibrosis
  • None of the animal studies drawn on had been designed to examine the fibrosis-tumor association

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: Fibrosis, Asbestos Exposure, Pulmonary Fibrosis, Carcinoma, Carcinogenic.

Related studies

• Other diseases in animals — J.M. Davis (1994)
• Pulmonary function and pleural fibrosis: quantitative relationships with an integrative index of pleural abnormalities — R. Lilis, A. Miller, et al. (1991)
• Radiographic abnormalities in asbestos insulators: effects of duration from onset of exposure and smoking. Relationships of dyspnea with parenchymal and pleural fibrosis — R. Lilis, A. Miller, et al. (1991)
• Asbestosis and other pulmonary fibrosis in asbestos-exposed workers: high-resolution CT features with pathological correlations — H. Arakawa, T. Kishimoto, et al. (2016)
• An experimental approach to the evaluation of the biopersistence of respirable synthetic fibers and minerals — D.M. Bernstein, R. Mast, et al. (1994)
• The long term fibrogenic effects of chrysotile and crocidolite asbestos dust injected into the pleural cavity of experimental animals — J.M. Davis (1970)

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