An oncogene is a gene that, when mutated or expressed at high levels, helps turn a normal cell into a tumor cell.
Many abnormal cells normally undergo a programmed form of death (apoptosis). Activated oncogenes can cause those cells to survive and proliferate instead. Most oncogenes require an additional step, such as mutations in another gene, or environmental factors, such as viral infection, to cause cancer.
Since the 1970s, dozens of oncogenes have been identified in human cancer. Many cancer drugs target those DNA sequences and their products.
The first oncogene was discovered in 1970 and was termed src (pronounced ''sarc'' as in ''sarcoma''). Src was in fact first discovered as an oncogene in a chicken retrovirus. Experiments performed by Dr G. Steve Martin of the University of California demonstrated that the SRC was indeed the oncogene of the virus.
In 1976 Drs. J. Michael Bishop and Harold E. Varmus of the University of California demonstrated that oncogenes were defective proto-oncogenes, found in many organisms including humans. For this discovery Bishop and Varmus were awarded the Nobel Prize in 1989.
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