Biological actions of oncogenes.

Cancer, in many cases, results from multistep genetic mutation. Certain genes can have a predisposed susceptibility to mutations that lead to cancer because of chromosome location or their importance in the control of cell cycles. Mutations that deregulate the expression or activity of enzymes involved in the biochemical pathways of growth and differentiation or that suppress the expression of negative cell cycle control factors result in activation of oncogenesis. The study of oncogenes and tumor suppressor genes has greatly influenced our understanding of the molecular origins of cancer. We focus here on the normal biological action of proto-oncogenes compared with the transforming activities of oncogenes and tumor suppressor genes, and we discuss possible mechanisms of oncogenic transformation.