<P> An oncogene is a gene that has the potential to cause cancer . In tumor cells, they are often mutated and / or expressed at high levels . </P> <P> Most normal cells will undergo a programmed form of rapid cell death (apoptosis) when critical functions are altered and malfunctioning . Activated oncogenes can cause those cells designated for apoptosis to survive and proliferate instead . Most oncogenes began as proto - oncogenes, normal genes involved in cell growth and proliferation or inhibition of apoptosis . If normal genes promoting cellular growth, through mutation, are up - regulated, (gain of function mutation) they will predispose the cell to cancer and are thus termed oncogenes . Usually multiple oncogenes, along with mutated apoptotic and / or tumor suppressor genes will all act in concert to cause cancer . Since the 1970s, dozens of oncogenes have been identified in human cancer . Many cancer drugs target the proteins encoded by oncogenes . </P>

1. a normal gene that if mutated can lead to cancer is called a(n)