Early animal research on asbestos cancer

Our plain-English summary of Early animal research on asbestos cancer, by P.E. Enterline (American Journal of Industrial Medicine, 1993).

The study

• Author: P.E. Enterline
• Journal: American Journal of Industrial Medicine
• Published: 1993;24(6):783-5; author reply 787-91
• Type of article: Letter
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This is a letter to the editor, not a research study. The author responded to a 1991 letter by Hardy and Egilman suggesting that Gardner and Vorwald suppressed results of mouse experiments with asbestos done at Saranac Laboratory in the 1940s and 1950s. Using letters and unpublished reports, the author described a 1943 outline in which Gardner reported 8 malignant lung tumors among 11 mice inhaling long asbestos fibers for 15-24 months. Gardner called this only suggestive evidence, citing an apparently unusually susceptible mouse strain, few survivors beyond 15 months and no unexposed controls of the same strain and age. A 1952 interim report by Vorwald found tumors in 9.5% of 179 exposed mice and 5.5% of 181 controls at 14 months. Vorwald said this difference was not statistically significant, and no final report has been found. The author suggested the tumors may have been adenomas and noted that mice are a poor model. The author concluded that the documents point to more probable reasons than suppression for why the data went unpublished.

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: Letter to the editor (commentary), replying to a 1991 letter by Hardy and Egilman. It reports no new data and draws on letters and unpublished reports the author had collected.
• Who was studied: No population was studied. The letter discusses unpublished animal (mouse) experiments carried out at Saranac Laboratory in the 1940s and 1950s by Gardner and later Vorwald.
• Exposure: Inhaled asbestos dust in mice, described as long and short asbestos fibers (fiber type not named for these experiments). A 1955 study by Schepers et al., also mentioned, used commercial hydrous silicate contaminated with chrysotile asbestos.
• Main results:
  • According to the author's account of Gardner's 1943 outline: 8 malignant lung tumors among 11 mice inhaling long asbestos fibers for 15-24 months, and 3 mice with lung tumors among 22 inhaling short fibers for less than 12 months.
  • Gardner regarded these observations as only suggestive. The reasons given were a mouse strain that was apparently unusually susceptible, too few animals surviving beyond 15 months, no unexposed controls of the same strain and age, and no similar controls exposed to other dust.
  • A 1948 draft report to Johns Manville stated that Gardner's experimental notes called the lesions adenomas rather than cancer. A revised report dated January 31, 1949 removed all references to tumors.
  • Vorwald's 1952 interim report covered 179 mice in the experimental group and 181 controls. At 14 months, 9.5% of the experimental animals and 5.5% of the controls had developed a tumor. Vorwald said this difference was not statistically significant. The author stated that no later report on this experiment has been found.
  • The author offered an alternative explanation to suppression: the difference may have disappeared or remained questionable as the experiment continued, and the tumors may have been adenomas.
  • The author cited a 1957 mouse study by Lynch et al. in which no tumors were considered malignant, and stated that the mouse is a poor model for human asbestos carcinogenesis. The first positive inhalation study of asbestos lung cancer, reported in 1967, involved rats.
  • Responding to a suggestion about the author's own 1978 editorial, the author stated that the editorial was essentially the 2-page conclusion of a 1978 manuscript. That manuscript was later privately printed in 1980.
• The authors' conclusion: The author concluded that the documents suggest other and more probable reasons why the Gardner-Vorwald animal data were never published. The author also wrote that if industry-sponsored researchers did suppress results, Egilman and Hardy need better examples.
• Limitations the authors state:
  • The author's argument rests on copies of letters and unpublished reports, which the author assumes to be valid.

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• Histogenesis and fine structure of peritoneal tumors produced in animals by injections of asbestos — J.M. Davis (1974)

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