Apparent increased risk of leukemia in their highest category of exposure to tetrachloroethylene (PCE) in drinking water.

The potential human carcinogenicity of PCE has been the subject of study for many years, yet the largest and most recent occupational studies have not reported any increased risk of leukemia in PCE-exposed groups, let alone a risk of the magnitude suggested by Aschengrau et al. The EPA's own Science Advisory Board concluded in 1991 that PCE is a chemical "for which there is no compelling evidence of human cancer risk, accompanied by animal data of carcinogenicity whose extrapolation to humans is ambiguous." Given this background, it is not plausible that a leukemia risk of the magnitude reported by Aschengrau et al. should exist but not have been found among highly exposed occupational groups. Aschengrau et al. could contribute to our understanding of this inconsistency by presenting the additional data analysis that I have suggested.