A search for chemical agents causing human cancer--lessons learned from rodent carcinogenicity studies

Analysis of classical life-time rodent bioassays conducted over the past 20 years under conditions of Good Laboratory Practice Regulations has led to an improved understanding of possible factors involved in oncogenesis in humans. Improvements in study design coupled with more detailed pathological examinations have led to new insights whereby neoplastic processes can be more clearly identified and understood with confidence in animal models. Improvements in the ability to identify potential risks through continued animal testing combined with incorporation of advances in genetics and molecular biology in elucidating mechanistic factors will greatly facilitate future research efforts to identify causative agents of human cancer. A great deal of attention will have to be paid to the concept of threshold doses and exposure levels that may be required to achieve preneoplastic conditions or the induction of carcinogenic processes. Future concerns of hazards, risk assessment and the evaluation of carcinogenic potential will involve an amalgamation and understanding of radiological and biological events, especially those of carcinogenic microorganisms, the effects of food and air borne carcinogens, effects of pollution, exposure to xenobiotics and imbalances and disruption of normal biologic functioning of endogenous physiologically active substances, to achieve a better understanding and ultimate prevention of human cancer.