Oncogenes.

Oncogenes were first identified in neoplastic tissues and were thought to be disseminated by retroviruses. They were shown to cause neoplastic transformation of cells in vitro and were therefore regarded as "the genes that cause cancer." They occur in all eukaryotes including humans. More than 30 oncogenes have been identified, and 28 have already been mapped to the human karyotype. When the protein products of the oncogenes were investigated, they were found to be very similar to known substances that are normally involved in the control of cell division--growth factors, plasma-membrane receptors, modulators of the transduction of exogenous signals through the plasma membrane, and nuclear DNA-binding substances. These discoveries changed the original concept of oncogenes. They are now regarded as playing vital roles in the normal control of mitosis, and they should properly be called mitogenes rather than "oncogenes." Like all other genes, if a mitogene is mutated, rearranged, translocated, or otherwise deranged, its effects will change; it may then become an oncogene that will promote disorderly cell division and thus contribute to the pathogenesis of cancer. In addition to providing new insights into the normal control of mitosis and its neoplastic transformation, the discovery of the mitogenes has suggested new approaches to the early diagnosis of cancer, to a more rational classification of neoplasms based on pathogenesis rather than morphology, and, perhaps, to more rational forms of therapy.