The subject of cancer risk assessment (S. Brudnoy, The Scientist, March 8, 1993, page 14) is of continuing interest to academic scientists, but even more important to regulatory agencies. This topic is not as controversial scientifically as some may make it. All human carcinogens are genotoxic; that is, they can react under suitable conditions with DNA and genes, a fact leading to analytical detection. An exception as a nongenotoxic human carcinogen is high levels of the hormone diethylstilbestrol-- DES. Two excellent rapid tests, the Ames test and the DNA repair test of Gary M. Williams, director of medical sciences at the American Health Foundation, provide key information on genotoxicity. Agents that are not genotoxic can play a role in cancer causation, but for such agents there is a sharp dose- response relationship, with a threshold. Thus, exposures at levels that sensitive analytical chemistry can detect in the environment are not...

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