ABSTRACT
This chapter shows that common molecular determinants may be responsible for tumors of both classes. These determinants, the cellular oncogenes, constitute a functionally heterogeneous group of genes, members of which may cooperate with one another in order to achieve the transformation of cells. An initial insight into cellular oncogenes came from study of Rous sarcoma virus (RSV). Retroviruses such as RSV have been studied intensively for the past decade, in part because of their unusual molecular biology involving reverse transcription and the high-efficiency integration of their genomes into the cellular chromosome. Many types of tumor cells develop transforming sequences in their DNA during their progression from the normal to the cancerous state. The proto-oncogenes and the proteins that they specify form a structurally and functionally heterogeneous group. The procedures of gene transfer and molecular cloning have made it possible to dissect out some of the centrally important determinants of the cancer process.
