A WEIBULL MODEL FOR THE ESTIMATION OF TUMORIGENIC POTENCY

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