Oncogenes.

SIGNIFICANCE: Oncogenes are mutated forms of normal genes that, when activated, can transform normal cells into cancerous cells. The prefix “onco-” comes from the Greek word meaning “tumor.” Oncogenes originate in normal cellular genes, often ones that help control cell division. When normal cells become damaged or have completed their functions, they commit suicide through a process called apoptosis. Cancer disrupts that process, causing cells in effect to pursue immortality. Proto-oncogenes, in contrast, are normal genes involved in controlling cell division that, if damaged by mutations, can become oncogenes. The term “proto-oncogene” is misleading in that it implies that progression into an oncogene is inevitable when in fact it is not. Proto-oncogenes lack the ability of oncogenes to transform cells.