An approach to the determination of the relative potencies of chemical agents during the stages of initiation and promotion in multistage hepatocarcinogenesis in the rat.

The potency of carcinogenic agents in eliciting neoplastic lesions has long been a concern of investigators in the field of oncology. This paper describes a method, based on quantitative stereologic calculations, to estimate the relative potency of chemicals as initiating and/or promoting agents. The parameters defined in this paper are: (a) Initiation index = no. foci induced X liver-1 X [mmole/kg body weight]-1; and (b) Promotion index = Vf/Vc X mmol-1 X wk-1. These parameters have been calculated for a number of chemical agents, based both on data from this laboratory and others published in the literature. Neither parameter varied significantly with the dose of two different initiating agents used in this study. The range of promotion indices extended over more than eight orders of magnitude, whereas that of the initiation indices was much less variable. Such parameters may be useful as quantitative estimates of the potency of hepatocarcinogenic agents not only in rodents, but potentially in quantitative risk estimations in the human.