A brief history of the use of laboratory animals for the prediction of carcinogenic risk for man with a note on needs for the future

This review discusses developments during the last 60 years in the field of carcinogenicity testing based on the use of laboratory animals. Improvements that have occurred in the quality of animals and in the way in which tests are conducted are considered, along with the importance of distinguishing between fatal and incidental tumours. Still to be faced is a need to control calorie intake in the course of carcinogenicity testing. A necessity for a better understanding of how disturbances of physiological and/or hormonal status can predispose to tumour development and for more comparative metabolism studies is stressed. Recognition of the fact that thresholds exist for carcinogenesis by nongenotoxic compounds poses a need for avoiding unrealistically high levels of exposure and for more and better information on how different species metabolise test agents.