Oncogene

• one of a small number of normal genes in vertebrates that are highly conserved evolutionarily and can cause cancer when they are mutant or inappropriately expressed
  Source: Jenkins, John B. 1990. Human Genetics, 2nd Edition. New York: Harper & Row
• A gene that contributes to cancer formation when mutated or inappropriately expressed.
• An oncogene is a mutated gene that contributes to the development of a cancer. In their normal, unmutated state, onocgenes are called proto-oncogenes, and they play roles in the regulation of cell division. Some oncogenes work like putting your foot down on the accelerator of a car, pushing a cell to divide. Other oncogenes work like removing your foot from the brake while parked on a hill, also causing the cell to divide.