Prediction of rodent carcinogenesis: An evaluation of prechronic liver lesions as forecasters of liver tumors in NTP carcinogenicity studies

The National Toxicology Program (NTP) developed the chronic 2-year bioassay as a mechanism for predicting the carcinogenic potential of chemicals in humans. The cost and duration of these studies has limited their use to small numbers of selected chemicals. Many different short-term methods aimed at increasing predictive accuracy and the number of chemicals evaluated have been developed in attempts to successfully correlate their results with evidence of carcinogenicity ( or lack of carcinogenicity). Using NTP studies, the effectiveness of correlating prechronic liver lesions with liver cancer encompassing multiple studies using mice ( 83 compounds) and rats (87 compounds) was assessed. These lesions include hepatocellular necrosis, hepatocellular hypertrophy, hepatocellular cytomegaly, bile duct hyperplasia, and hepatocellular degeneration, along with increased liver weight. Our results indicate that pooling 3 of these prechronic data points ( hepatocellular necrosis, hepatocellular hypertrophy, and hepatocellular cytomegaly) can be very predictive of carcinogenicity in the 2-year study (p < 0.05). The inclusion of increased liver weight as an endpoint in the pool of data points increases the number of rodent liver carcinogens that are successfully predicted ( p < 0.05), but also results in the prediction of increased numbers of noncarcinogenic chemicals as carcinogens. The use of multiple prechronic study endpoints provides supplementary information that enhances the predictivity of identifying chemicals with carcinogenic potential.