Availability of epidemiologic data for chemicals known to cause cancer in animals: an update

Our plain-English summary of Availability of epidemiologic data for chemicals known to cause cancer in animals: an update, by M. Karstadt (American Journal of Industrial Medicine, 1998).

The study

• Author: M. Karstadt
• Journal: American Journal of Industrial Medicine
• Published: 1998;34(5):519-25
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Between 1972 and 1996, the International Agency for Research on Cancer (IARC) identified 282 chemicals as having experimental evidence "sufficient" to conclude that the chemicals cause cancer in animals. Of the 282 IARC animal carcinogens, 7% (20) also had "sufficient" evidence from epidemiology studies. "Limited" human evidence was available for 5% (13) of the 282 IARC animal carcinogens. A 1996 IARC international compendium of cancer studies indicated that epidemiologic studies of chemicals determined by IARC to cause cancer in both humans and animals were considerably more common than studies of chemicals determined to cause cancer in animals but for which human data were inadequate or limited. Of the 1,101 studies reported to IARC by investigators, the IARC animal carcinogens, with the most ongoing studies were asbestos (50 studies) and benzene (26 studies). Both chemicals have sufficient evidence of carcinogenicity from studies of humans. There were epidemiologic studies ongoing for 65% (13/20) of the chemicals for which evidence of carcinogenicity was sufficient in both animals and humans. Epidemiologic studies were reported to IARC for 12% (30/247) of the IARC animal carcinogens for which human data were inadequate or for which no human data were available. Two factors appear critical in determining whether an IARC animal carcinogen becomes the subject of an epidemiologic study: the likelihood of overcoming methodological obstacles to carrying out successful epidemiologic studies, and the economic and/or regulatory interest in the chemical.

In plain English

This commentary updated a 1981 review by the author and colleagues. The author searched International Agency for Research on Cancer (IARC) monographs from 1972 to 1996 for chemicals with sufficient evidence of causing cancer in animals. The author also searched IARC's 1996 directory of ongoing studies. Of these 282 animal carcinogens, 20 (approximately 7%) also had sufficient evidence from human studies, and 13 had limited human evidence. The directory listed 1,101 research projects. The animal carcinogens with the most ongoing studies in the directory already had sufficient human evidence: asbestos (50 studies), benzene (26, though one table gives 24) and chromium and certain chromium compounds (22). The asbestos entries included amosite, chrysotile, crocidolite and tremolite studies. Of 247 animal carcinogens with inadequate or no human data, 30 (12%) were listed in the directory as being studied. The author suggested asbestos may be easier to study because of its rare marker cancer, mesothelioma. The author concluded that the share of animal carcinogens also shown to cause cancer in humans was very low. The author noted the directory relied on voluntary reports.

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: Commentary updating an earlier review: a review of IARC monograph evaluations and of IARC's directory of ongoing epidemiologic studies
• Who was studied: 282 chemicals designated by IARC as animal carcinogens (sufficient animal evidence) in IARC monograph volumes 1 to 66 (1972 to 1996), plus the research projects listed in the 1996 IARC Directory of On-Going Research in Cancer Epidemiology
• Exposure: All chemicals IARC designated as animal carcinogens, including asbestos. In the directory, asbestos studies were listed as asbestos not otherwise specified, amosite, chrysotile, crocidolite and tremolite. Benzene and chromium and certain chromium compounds were also among them.
• Main results:
  • Of all 282 IARC animal carcinogens, 20 (approximately 7%) had sufficient human evidence as of late 1996
  • Of the 145 chemicals identified as IARC animal carcinogens after supplement 1 (1979), human data were considered sufficient for 5, or 3%
  • 13 IARC animal carcinogens had limited human evidence in volumes 1 to 66, and 10 of these were subjects of studies reported to the directory
  • Among the 1,101 projects in the 1996 directory, the IARC animal carcinogens with the most ongoing studies were ones already judged to have sufficient human evidence: asbestos (50 studies), benzene (26 studies in the discussion text and Table IV, but 24 in Table VI), and chromium and certain chromium compounds (22 studies)
  • Table VI gives a different benzene total of 24 studies
  • The 50 asbestos studies were listed as 41 on asbestos not otherwise specified, 1 on amosite, 4 on chrysotile, 3 on crocidolite and 1 on tremolite
  • Of the 247 IARC animal carcinogens with inadequate or no human data, 12% (30 of 247) were identified in the 1996 directory as subjects of ongoing epidemiologic studies
  • The author noted that an ongoing chrysotile asbestos study at McGill University was part of a research program supported by a Quebec asbestos industry association
  • The author suggested that some chemicals with sufficient human evidence may be easier to study; for asbestos, the author pointed to mesothelioma as a rare marker cancer
• The authors' conclusion: The author concluded that the percentage of IARC animal carcinogens also considered carcinogenic in humans based on human evidence is very low. The author also concluded that methodological obstacles and economic considerations may continue to skew studies toward chemicals already shown to cause cancer in human studies.
• Limitations the authors state:
  • The IARC directory relies on voluntary submissions, so it is difficult to know how fully it reflects all ongoing epidemiologic studies
  • Industry may be the sector least well represented in the directory
  • Study sponsors are not identified in the directory, so industry-sponsored studies at academic institutions are hard to identify

Topics

Medical terms in this study, explained in our Lexicon: IARC, Epidemiology.

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