Meta-analyses of TCE carcinogenicity.

We read with interest the recent report by Wartenberg et al. (1) in which they described an “ad hoc system” and “meta-analysis–type approach” for evaluating the carcinogenicity of trichloroethylene (TCE). In particular, we are concerned that their methods may obscure rather than clarify the relationship between TCE and human cancer. Briefly, Wartenberg et al. (1) categorized studies on the basis of their design: cohort, case–control, community-based, and case series. Cohort studies were then divided “into three tiers based on the specificity of the exposure information” contained in each. Next, the authors estimated the average relative risk for each tier, which was calculated using