Anticarcinogencity and Interpretation of Long-Term Rodent Bioassays. G. M. Gray, Harvard Center for Risk Analysis, 718 Huntington Ave., Boston, MA 02115; and I. Linkov and R.Wilson, Department of Physics, Harvard University, Cambridge, MA 022138
For over 25 years regulatory agencies have used rodent bioassays to provide evidence for chemical carcinogenicity and for quantitative risk assessment of chemicals. This procedure has come under increasing scrutiny. On one hand, some experts argue that animal tests are subject to so many flaws as to be useless. On the other, extreme proponents steadfastly refuse to change procedures that have been "#34 used for 25 years. In the middle many scientists point out results from studies of the large number of rodent bioassays conducted that generate hypotheses about mechanisms with important implications for risk assessment. One factor rarely considered in evaluation of rodent bioassays is anticarcinogenicity. We find that many tested chemicals reveal at least one site with a significant tumor rate decrease in one or more tested groups. Although long recognized, these anticarcinogenic responses have typically been discounted as artifacts of random variability in the background tumor rates, decreases in body weight or decreases in survival of treated animals. We have investigated each of these potential explanations for anticarcinogenicity and conclude that it is likely that much anticarcinogenicity is due to real biological effects. Our results suggest that the anticarcinogenic responses observed in rodent cancer bioassays should be carefully considered in evaluations of the overall carcinogenic potential of chemicals.
Work partially supported by the Elsa U. Pardee Foundation.
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