THE CONTRIBUTION OF THE MOUSE IN HAZARD IDENTIFICATION STUDIES

Because there is usually more extensive toxicity, metabolism, and phar macokinetic information for pharmaceuticals as opposed to environmenta l agents, including pesticides, the argument has been made that carcin ogenicity testing in two rodent species may not have been necessary fo r carcinogenicity testing of pharmaceuticals. On the basis of numerica l data only, it may be argued that carcinogenicity testing of pharmace uticals in one species, typically the rat, is sufficient to identify p otential human carcinogens. The argument that testing in a second spec ies, typically the mouse, is redundant overlooks the value added by th e second species carcinogenicity study. Bioassay data from the second species allows balance and perspective in evaluating the observed effe cts, and this is especially critical when there is a marginal, questio nable, or inconclusive response in one species. Utilization of two spe cies for carcinogen identification is the principal means for identify ing trans-species carcinogens-those mostly likely to be carcinogenic i n humans. Given that neither rat nor mouse are ideal surrogates for hu mans, concordant data from both species strengthens the ability to ext rapolate findings to humans. We believe that testing in two species sh ould continue to be the default approach used for carcinogen hazard id entification whenever scientifically indicated until such time that ac ceptable and suitable alternatives are available. To utilize only one species for this important means of protecting human health is prematu re at this time.