on·co·gene 
(ŏnkə-jēn, ŏng-)
(ŏnkə-jēn, ŏng-)n.
1. Any of various mutated genes that cause the transformation of normal cells into cancerous cells.
2. Any of various viral genes that transform host cells into cancerous cells.
[Greek onkos, mass, tumor; see ONCOLOGY + GENE.]