An empirical comparison of methods used to estimate carcinogenic potency in long-term animal bioassays: lifetable vs summary incidence data.

Two methods for estimating carcinogenic potency from animal carcinogenesis bioassays (TD50-defined in the paper) are compared, one based on lifetable data and one based on summary incidence data. The lifetable analysis adjusts for the differential effects of toxicity among dose groups and for differences in the time pattern of tumor incidence, while summary incidence analysis does not. However, summary data are all that are usually available in the published results of animal cancer tests. Using NCI bioassay results which provide full lifetable data, we compare lifetable and summary estimates of potency and their statistical significance as well as the estimated shape of the dose-response curve. There is substantial agreement between these methods of analysis in terms of potency estimation, although lifetable estimates are usually more potent. But, there are some notable differences in the estimated shape of the dose-response curve, suggesting that both target site selection and method of analysis play an important role in risk estimation.