ABSTRACT
Multistep theories of carcinogenesis assume that cancer develops from a single normal stem cell that has undergone a series of irreversible and heritable changes related to the cell’s release from growth control and its ability to invade other tissue. This chapter aims to develop a multiple–pathway stochastic model for the carcinogenesis process and deals with multiple– pathway models involving only one– and two–stage models. It provides some specific biological evidences for the proposed model and also provides the probability generating function of the number of tumor cells under some general conditions. The chapter derives the incidence functions of the tumors and provides an iterative procedure to compute the probabilities of the number of tumors. It aims to point out that in developing risk assessment procedures for multiple–pathway models, one might face some problems of estimating unknown parameters, especially the number of two–stage pathways. Much evidence exists indicating that normal stem cells become immortalized by the loss of differentiation capability.
