Use of 'secondary mechanism' in the regulation of carcinogens; a chronology.

Significantly more willingness to depart from worst case assumptions in the evaluation of carcinogenic risk has developed in the last 30 years. Scientists within regulatory agencies and in the academic community are reaching a consensus on the inadequacy of current test methods and on the need for more mechanistic data to help interpret the carcinogen bioassay. The slow regulatory acceptance of the concept of 'secondary mechanism' in the evaluation of cancer risk from chemicals in the U.S. is illustrated by a chronology of laws, policies, and consensus scientific positions adopted through the years.