Growth factors, oncogenes, and multistage carcinogenesis.

This paper presents evidence that the full repertoire of cellular genes involved in the carcinogenic process is several times larger than that of the known list of proto-oncogenes. Furthermore, this repertoire includes genes whose normal function is related to growth stimulation, as well as genes whose normal function is to inhibit growth or induce terminal differentiation. Multistage carcinogenesis probably results from a complex series of changes in both categories of genes. Despite this complexity, carcinogenesis can be conceived in terms of disturbances in biochemical functions that normally control the expression or function of growth factors, receptors, and pathways of signal transduction. Several protein kinases play a central role in the process of signal transduction. Our laboratory has recently isolated cDNA clones for the enzyme protein kinase C (PKC). These clones should be useful for clarifying the role of PKC in growth control and tumor promotion. Finally, the existence of genes whose normal function is to inhibit cell growth provides a rationale for new strategies of cancer prevention and treatment.