The committee was charged with developing carcinogenic risk estimates for different magnitudes of inhalation exposure to beryllium. However, the committee judged that the available human and animal data are inadequate to support a dose-response analysis with low-dose extrapolation to current exposure level magnitudes. Several critical questions needed to characterize a dose-response relationship cannot be answered now. Those questions include
What physicochemical characteristics and particle sizes are associated with beryllium-induced cancer?
Is cancer risk driven by peak exposures, by cumulative exposures, or by other dose metrics?
How have earlier and later exposures of beryllium workers to other lung carcinogens affected disease incidence?
How have changes in workplace practices affected the ability to identify dose-response relationships?
Is there an animal model in which beryllium induces lung cancer by the same mode of action as in humans?
The committee concludes that a meaningful cancer dose-response assessment cannot be conducted until more information is available on existing or new worker cohorts: complete work history, possible exposure to other carcinogens, and better exposure histories. It may also be necessary to investigate mode of action further with animal studies if a suitable model can be identified. Such studies could help to elucidate the relative importance of peak vs cumulative exposures in cancer incidence.
Furthermore, carcinogenic risk estimates would be of limited utility in light of the committee’s recommended approach to preventing beryllium disease. The committee found that it is not possible to reliably identify an exposure magnitude at which there is no risk of sensitization and development of CBD and therefore recommended that the Air Force implement a surveillance and medical-monitoring program to keep exposure as low as feasible to prevent adverse health effects. Recommendations for designing such a program are presented in Chapter 7.