Molecular analysis of chemical carcinogenesis in the skin.

The goal of understanding the molecular basis of human tumour development has been greatly facilitated by the use of animal model systems in which the aetiology of tumour development can be carefully controlled. Environmental chemicals, either naturally occurring or artificially produced, are thought to make a major contribution to the human tumour burden. The process of carcinogenesis can be divided operationally into the stages of initiation, promotion and progression and many different classes of chemical agents can act at one or more of these stages. Many of the concepts of multistage carcinogenesis have been developed and refined using the mouse skin model system and most of the work to be described in this article has been carried out in an attempt to analyse the molecular changes which are associated with the initiation of tumour development, the selection of initiated cells to form papillomas or the progression of premalignant tumours to carcinomas.