Risk assessment of carcinogens: present status and future directions.

Regulatory agencies and public health authorities make extensive use of laboratory data on chemical carcinogenicity in the establishment of acceptable human exposure standards. Risk assessment practices require the quantitative extrapolation of animal data to the human setting. In this paper, the scientific assumptions underlying risk assessment are evaluated and future research needs are identified. Consideration also is given to the role of promotion assays in the evaluation of carcinogenesis and the part played by short-term tests for carcinogenicity in the regulatory process.