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Asbestos Selected Cancers (2006) / Chapter Skim
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Pages 1-12

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From page 1...
... Board on Population Health and Public Health Practices will oversee a study that will comprehensively review, evalu ate, and summarize the peer-reviewed scientific and medical literature regard ing the association between asbestos and colorectal, laryngeal, esophageal, pha ryngeal, and stomach cancers. Based on its examination and evaluation of the extant literature and other information it may obtain in the course of the study, the committee will determine if there is a causal association between asbestos and colorectal, laryngeal, esophageal, pharyngeal, or stomach cancers.
From page 2...
... The committee was aware that fiber type may be a determinant of risk of developing mesothelioma (and possibly lung cancer) following asbestos exposure.
From page 3...
... The reviews of the evidence related to mineralogy of asbestos and to its carcinogenicity were considered to be generally relevant for all sites, particularly in regard to the causal criterion of coherence or biologic plausibility. There has been ongoing discussion as to whether there is an absolute difference in the toxicity of the major fiber types, serpentine and amphibole, and whether only amphibole fibers have carcinogenic potential, particularly for mesothelioma, the neoplasm for which the evidence is most suggestive of a difference in risk by fiber type.
From page 4...
... Fibers deposited in the lung are cleared by the mucociliary apparatus, and swallowing of asbestos-containing mucus causes it to pass through the gastrointestinal tract and can lead to potential exposure of the esophagus, stomach, colon, and rectum to asbestos fibers. Encapsulated fibers, known as asbestos bodies, are routinely found in the respiratory tissues of asbestos-exposed individuals; although they have not been systematically sought in other organs, there have been some reports of finding asbestos bodies in extrapulmonary tissues, including the portions of the gastrointestinal tract addressed in this report.
From page 5...
... Pharyngeal Cancer The committee reviewed six case-control studies of pharyngeal cancer, four of which had exposure assessments of high quality or adjusted for confounding, and the findings on 16 cohort populations. Although the information from the case-control studies was very sparse, the aggregated risk estimate for any asbestos exposure was modest and similar to that for the more numerous cohort studies.
From page 6...
... The committee found consistency of findings among the epidemiologic studies. Asbestos exposure was associated with increased risk of laryngeal cancer in the nine larger cohort studies and in meta-analyses of the cohort and case-control data.
From page 7...
... The committee concluded that the evidence is sufficient to infer a causal relationship between asbestos exposure and laryngeal cancer. Esophageal Cancer Both case-control and cohort studies of esophageal cancer were reviewed, but the available body of evidence was limited.
From page 8...
... Six animalfeeding studies did not find an association with esophageal cancer, and there is no other experimental evidence that asbestos fibers act as a direct or indirect carcinogen specifically in the esophagus. Some studies have found an association between asbestos exposure and esophageal cancer, but the overall results of epidemiologic studies are mixed.
From page 9...
... The committee concluded that the evidence is suggestive but not sufficient to infer a causal relationship between asbestos exposure and stomach cancer. Colorectal Cancer The committee evaluated the overall evidence on colorectal cancer because its charge addressed cancers of the colon and rectum together.
From page 10...
... The committee considered the existing evidence from in vitro and animal experimentation to gain an understanding of mechanisms of carcinogenesis that might plausibly apply to the tissues in question and to determine the extent of toxicologic support for the development of cancers at the specified sites following asbestos exposure. Much of the information reviewed by the committee came from cohort studies of workers that focused on investigating respiratory effects and that reported information on risks of other diseases, including the cancers covered by this committee's charge, only incidentally.
From page 11...
... Consideration should be given to approaches to strengthen the epidemiologic information on asbestos exposure and risk of cancer at the sites in the committee's charge. Information might be gained from further follow-up of some of the cohorts of asbestos-exposed workers; however, the committee is concerned that further study of these cohorts may be impossible because most were initiated decades ago and their records may not have been maintained.


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