Trends in incidence of mesothelioma and evaluation of exposure to asbestos

We describe, analyze, and contrast historical trends in mesothelioma cases in the U.S. and the U.K., and discuss these trends in relation to trends in asbestos exposure over the past 60 years. In the U.S., the number of mesot helioma cases for men is projected to have peaked at approximately 2,300 ca ses per year before the year 2000. On the basis of the historical trend and assumptions concerning current and projected exposure to asbestos, the ann ual number of male cases in the U.S. is projected to decline to the backgro und rate of approximately 500 cases per year around the year 2055. The time -dependent pattern for the number of female cases in the U.S. has been cons tant at approximately 500 cases per year and is projected to remain at that level. In the U.K., the number of male cases is projected to peak in the y ear 2020 somewhere between 2700 and 3300 cases per year depending on assump tions concerning asbestos exposure for men born after 1958. The time-depend ent pattern of female cases in the U.K. mirrors the pattern for males, but at a lower level. The 20-year difference in the timing of the peak occurren ce of cases between the U.S. and the U.K. may be explained by a 20-year dif ference in the timing of peak exposures. We briefly address the interpretat ion of these trends in order to differentiate the mesothelioma potency of a mphibole fibers from that of chrysotile fibers. We conclude, on the basis o f trends and exposure projections for the U.S., that the amphibole-chrysoti le debate has little practical significance for risk management if exposure s to asbestos continue to be maintained at the low levels of today.