Oncogene

An oncogene is a gene that has been changed in a way that helps convert a normal cell into a cancer cell. Its healthy version is called a proto-oncogene. Proto-oncogenes code for proteins that tell cells to grow and divide, such as growth factors, their receptors, signaling proteins and transcription factors, and they are needed for normal development and tissue repair.

A proto-oncogene becomes an oncogene through a gain-of-function change: a point mutation that locks its protein in the on state, extra copies of the gene, or a rearrangement that places it under a stronger control switch. The effect resembles an accelerator stuck down, driving the cell through the cell cycle when it should rest. Because the altered protein is overactive, a change in just one of the two copies can be enough. Most oncogene mutations arise during a person's lifetime rather than being inherited.

Oncogenes were first discovered in viruses that cause tumors in animals; these viruses turned out to carry altered copies of normal host genes. A well-known human example is HER2, a receptor that is overactive in some breast cancers and is the target of specific drugs.