PREDICTIONS FOR THE OUTCOME OF RODENT CARCINOGENICITY BIOASSAYS - IDENTIFICATION OF TRANSSPECIES CARCINOGENS AND NONCARCINOGENS

Thirty chemicals or substances currently undergoing long-term carcinog enicity bioassays in rodents have been used in a project to further ev aluate methods and information that may have the capability of predict ing potential carcinogens. In our predictions the principal informatio n used includes structural alerts and in vitro test results for Salmon ella mutagenicity, relative subchronic toxicity, and the sites and typ es of pathology found in subchronic (90-day) studies. This group of ch emicals differs significantly from those used previously to evaluate p redictive methods in that 23 of 30 are defined as nonmutagenic by conv entional criteria. The goal of this predictive effort is to identify c ategorically the chemicals that have the capacity to induce cancers in both rats and mice (trans-species carcinogens) and those that are not carcinogenic in either rats or mice. Chemicals that show properties t hat may be associated with tumor induction in either species, i.e., sp ecies-specific cancers, are categorized as being of ''uncertain predic tability.'' This category includes chemicals believed to have limited carcinogenic potential that is manifested principally as a consequence of the genetic background of the test strain of inbred rodent.