This committee was charged with reviewing evidence on a widely used material that is known to cause respiratory malignancy. Asbestos has been extensively investigated as a cause of mesothelioma and lung cancer with epidemiologic and experimental approaches. However, its potential to cause malignancy at other sites that may also be exposed to substantial numbers of asbestos fibers has not been as extensively investigated; little effort has gone into determining delivered or effective dose at these extrapulmonary sites. Much of the information reviewed by the committee came from cohort studies of workers that focused on investigating respiratory effects; information on risks of other diseases, including cancers at the site covered by this committee’s charge, was reported only incidentally. Other evidence came from case-control studies directed at the causes of the cancers at the sites of interest, but these studies were not specifically designed to address asbestos exposure and their exposure assessments varied in quality.
The committee’s review identified limitations of the available evidence that contributed uncertainty to its conclusions. Although the committee was not charged with developing a research agenda to address the information gaps, its review found many research needs. Research should address the relevance of physical and chemical characteristics of asbestos fibers to carcinogenicity. Studies directed at doses of fibers received by organs other than the lung are needed; mechanistic studies directed at these organs could prove to be a useful complement to ongoing work on the respiratory carcinogenicity of asbestos fibers. Studies involving animal models with high risk for cancer of the designated sites might also be useful. In addition, consideration should be given to approaches to strengthen the epidemiologic information on asbestos exposure and risk of cancers 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 no longer be possible in that most were initiated decades ago and their records may not have been maintained. Some effort might be made to determine whether key cohorts could be followed up or new studies started on potentially informative populations.