Common gene variations Oncogene a gene with the potential to cause cancer often mutated or expressed at high levels in tumor cells Proto-oncogene a normal gene that can become an oncogene due to mutations or increased expression coding for proteins that help to regulate cell growth and differentiation anti-oncogene, or tumor suppressor gene a gene protecting a cell from one step on the path to cancer When mutated to cause a loss or reduction in its function the cell can progress to cancer in combination with other genetic changesCommon gene variations Oncogene • a gene with the potential to cause cancer • often mutated or expressed at high levels in tumor cells Proto-oncogene • a normal gene that can become an oncogene due to mutations or increased expression • coding for proteins that help to regulate cell growth and differentiation anti-oncogene, or tumor suppressor gene • a gene protecting a cell from one step on the path to cancer • when mutated to cause a loss or reduction in its function, the cell can progress to cancer in combination with other genetic changes