An oncogene is a gene that causes cancer.
DNA is often called the molecule of life. Small coding sequences along a strand of DNA are called genes. Genes control all the functions of the body. While all the genes a person will ever need are present in all cells, they are not all active at the same time. Genes that control growth and development, for instance, are active only at certain times of life. The rest of the time they are inactive.
Inactive genes are part of the human genetic make-up. Sometimes, however, a gene that controls growth and should be inactive is stimulated to do its work. If the work is done at an inappropriate time, cells multiply at random and a cancer may develop. The inactive gene is called a proto-oncogene. When it is activated it is called an oncogene.
Oncogenes act by producing normal signals at the wrong time. Oncogenes may work alone or together with other oncogenes. Some oncogenes act early in the process of tumor formation, while others act later. Some are initiators, which start the process, and others are promoters that increase the tumor growth.
Proto-oncogenes are converted to oncogenes by a number of factors, including: radiation, viruses, and certain chemicals in the environmentchanges in genesmutations, or changes, within the DNA moleculea gene that is repeated many times for an unknown reasonbreaks or rearrangements of chromosomes
Sometimes an unrelated gene, called a tumor suppressor, may be lost or inactivated. When this happens, proto-oncogenes are changed into oncogenes and cancer develops. Several dozen oncogenes have been identified, such as HER2NEU in breast cancer. Research into oncogenes has helped healthcare professionals understand why some people get cancer and others do not.
Research is continuing to identify more oncogenes and develop treatments to help control the damage they cause. Persons with cancer have had their proto-oncogenes converted into oncogenes. Those who have not yet developed cancer have not undergone this conversion. In other words, some people are more likely to develop cancer. Cancer-causing agents are more harmful to these people than to others.
King RA, Rotter JL and Motulsky AG: The Genetic Basis of Common Disease. Oxford University Press, 1992.