A Weibull model for the estimation of tumorigenic potency.

In this paper, a new method of estimating tumorigenic potency is proposed that takes into account information on survival and, when available, the underlying cause of death. Specifically, Weibull distributions are used to describe the time to tumor occurrence (X), the time to death as a result of tumor occurrence (Y), and the time of death from causes other than tumor occurrence (Z). The distributions of X and Y are related via a lethality parameter p lying between 0 (incidental tumors) and 1 (rapidly fatal tumors). The index of tumorigenic potency is defined as the dose inducing a specified excess tumor response rate (in the range of 25%-50%) following exposure for an extended period encompassing most of the expected lifespan. Application of the proposed method is illustrated using several data sets taken from the literature.