The Problem of Pseudocarcinogenicity in Rodent Bioassays

Pseudocarcinogenicity is defined as the enhancement of tumor risk by a nongenotoxic mechanism in physiologically abnormal animals. In the case of rats, severe endocrine disturbance secondary to overfeeding is the commonest cause of physiological abnormality. Pseudoanticarcinogenicity is the counterpart of pseudocarcinogenicity. The literature abounds with, and is seriously confused by, examples of these phenomena, which could be largely avoided by sensible choice of animal strain and intelligent animal husbandry. The fact that pseudocarcinogenic effects are reported alongside true carcinogenic effects while pseudoanticarcinogenic effects are usually ignored not only adds to the confusion, but also introduces serious bias into the overall picture.