Factors in the evaluation of 200 National Cancer Institute carcinogen bioassays.

In determining the carcinogenicity of chemical tested in a National Cancer Institute (NCI) bioassay, the following criteria are considered: (1) the adequacy of the bioassay data, (2) the presence of significantly increased incidences of tumor, (3) the adequacy of the number of animals at risk of developing tumors, (4) the adequacy of the dose of chemical administered, (5) the etiology and pathogenesis of the lesions, and (6) other factors that may influence an evaluation, such as a shortened latency period for tumor formation in dosed animals or the stability of the chemical. A decision tree for evaluating these factors is presented. A summary of the results of 200 NCl carcinogen bioassays is also reported. These procedures are presented in the hope that they may serve as discussion points for future developments in the field.