Identification and definition of chemical carcinogens: review of criteria and research needs.

Advances in carcinogenesis research have greatly improved the methods for detection, investigation, and definition of occupational carcinogens. A basis of scientific criteria has been developed for carcinogen identification and evaluation. Research, legislative, and regulatory initiatives in the United States are reviewed. The 1979 Report of the Working Group on Occupational Carcinogenesis, Occupational Cancer Task Force, National Cancer Institute, is added as an appendix. A detailed discussion is given of the 1979 report of the Interagency Regulatory Liaison Group entitled "Scientific bases for identification of potential carcinogens and estimation of risks." Two separate approaches are considered, i.e., the qualitative determination that a substance poses a carcinogenic hazard and the quantitative estimation of risk. The qualitative criteria are reviewed in the present paper. The need for critical data evaluation and the judgmental nature of the process are emphasized. Research needs arising from the analysis of these criteria are discussed. Laboratory research contributions to the identification and characterization of carcinogens are summarized, including development and study of organ target models for carcinogenesis in animals; studies of human target tissues and cells in culture; studies of transformation, initiation, and promotion of epidermal cells in culture; studies of transplacental carcinogenesis; and studies of molecular mechanisms.