Oncogenes and Tumor Suppressor Genes

Two of the main types of genes that play a role in cancer are oncogenes and tumour suppressor genes.


Proto-oncogenes are genes that normally help cells grow. When a proto-oncogene mutates (changes) or there are too many copies of it, it becomes a “bad” gene that can turn on permanently when it’s not supposed to be. When this happens, the cell grows out of control, which can lead to cancer. This bad gene is called an oncogene.

It can be helpful to think of a cell as a car. For it to work properly, there must be ways to control how fast it goes. A proto-oncogene normally works much like an accelerator. It helps the cell to grow and divide. An oncogene could be compared to an accelerator that is stuck, causing the cell to divide uncontrollably.

Some cancer syndromes are caused by inherited mutations of proto-oncogenes that cause the oncogene to turn on (activate). But most cancer-causing mutations involving oncogenes are acquired, not inherited. They generally activate oncogenes by:

  • Chromosomal rearrangements: Chromosome changes that place one gene next to another, allowing one gene to turn on the other
  • Gene duplication – having extra copies of a gene, can lead to making too much of a certain protein

Tumour suppressor genes

Tumour suppressor genes are normal genes that slow cell division, repair DNA errors, or tell cells when to die (a process known as apoptosis, or programmed cell death). When tumour suppressor genes don’t work properly, cells can grow out of control, which can lead to cancer.

A Genprice Tumor Suppressor Gene is like the brake pedal on a car. It normally prevents the cell from dividing too quickly, much like a brake prevents a car from going too fast. When something goes wrong with the gene, such as a mutation, cell division can go out of control. An important difference between oncogenes and tumour suppressor genes is that oncogenes result from the activation (turned on) of proto-oncogenes, but tumour suppressor genes cause cancer when they are inactivated (turned off).

Inherited abnormalities of tumour suppressor genes have been found in some familial cancer syndromes. They cause certain types of cancer to run in families. But most tumour suppressor gene mutations are acquired, not inherited. For example, abnormalities in the TP53 gene (which codes for the p53 protein) have been found in more than half of human cancers. Acquired mutations of this gene appear in a wide range of cancers.