Your genes are made of sequences of DNA that contain the information necessary for your cells to function and grow properly. Genes contain instructions (codes) that tell a cell to make a specific type of protein. Each protein has a specialized function in the body.

A proto-oncogene is a normal gene found in the cell. There are many proto-oncogenes. Each one is responsible for making a protein involved in cell growth, division, and other processes in the cell. Most of the time, these genes work the way they are supposed to, but sometimes things go wrong.

If an error (mutation) occurs in a proto-oncogene, the gene can become turned on when isn’t supposed to be turned on. If this happens, the proto-oncogene can turn into a malfunctioning gene called an oncogene. Cells will start to grow out of control. Uncontrollable cell growth leads to cancer.

Proto-oncogenes are normal genes that help cells grow. An oncogene is any gene that causes cancer.

One of the main characteristics of cancer is uncontrolled cell growth. Because proto-oncogenes are involved in the process of cell growth, they can turn into oncogenes when a mutation (error) permanently activates the gene.

In other words, oncogenes are mutated forms of proto-oncogenes. Most, but not all, oncogenes in the body arise from proto-oncogenes.

Proto-oncogenes are a group of normal genes in a cell. They contain the necessary information for your body to make the proteins responsible for:

  • stimulating cell division
  • inhibiting cell differentiation
  • preventing apoptosis (cell death)

These processes are essential for cell growth and development and for maintaining healthy tissues and organs in your body.

A proto-oncogene can’t cause cancer unless a mutation occurs in the gene that turns it into an oncogene.

When a mutation occurs in a proto-oncogene, it becomes permanently turned on (activated). The gene will then start to make too much of the proteins that code for cell growth. Cell growth occurs uncontrollably. This is one of the defining features of cancerous tumors.

Everyone has proto-oncogenes in their body. In fact, proto-oncogenes are necessary for our survival. Proto-oncogenes only cause cancer when a mutation occurs in the gene that results in the gene being permanently turned on. This is called a gain-of-function mutation.

These mutations are also considered dominant mutations. This means that only one copy of the gene needs to be mutated in order to encourage cancer.

There are at least three different types of gain-of-function mutations that can cause a proto-oncogene to become an oncogene:

  • Point mutation. This mutation alters, inserts, or deletes only one or a few nucleotides in a gene sequence, in effect activating the proto-oncogene.
  • Gene amplification. This mutation leads to extra copies of the gene.
  • Chromosomal translocation. This is when the gene is relocated to a new chromosomal site that leads to higher expression.

According to the American Cancer Society, most of the mutations that cause cancer are acquired, not inherited. This means that you aren’t born with the gene error. Instead, the change happens at some point during your life.

Some of these mutations result from an infection with a type of virus called a retrovirus. Radiation, smoke, and other environmental toxins may also play a role in causing mutation in proto-oncogenes. As well, some people are more susceptible to mutations in their proto-oncogenes.

Over 40 different proto-oncogenes have been discovered in the human body. Examples include:


The first proto-oncogene to be shown to turn into an oncogene is called Ras.

Ras encodes an intracellular signal-transduction protein. In other words, Ras is one of the on/off switches in a series of steps in a major pathway that eventually leads to cell growth. When Ras is mutated, it encodes for a protein that causes an uncontrolled growth-promoting signal.

Most cases of pancreatic cancer have a point mutation in the Ras gene. Many cases of lung, colon, and thyroid tumors have also been found to have a mutation in Ras.


Another well-known proto-oncogene is HER2. This gene makes protein receptors that are involved in the growth and division of cells in the breast. Many people with breast cancer have a gene amplification mutation in their HER2 gene. This type of breast cancer is often referred to as HER2-positive breast cancer.


The Myc gene is associated with a type of cancer called Burkitt’s lymphoma. It occurs when a chromosomal translocation moves a gene enhancer sequence near the Myc proto-oncogene.

Cyclin D

Cyclin D is another proto-oncogene. Its normal job is to make a protein called Rb tumor suppressor protein inactive.

In some cancers, like tumors of the parathyroid gland, Cyclin D is activated due to a mutation. As a result, it can no longer do its job of making the tumor suppressor protein inactive. This in turn causes uncontrolled cell growth.

Your cells contain many important genes that regulate cell growth and division. The normal forms of these genes are called proto-oncogenes. The mutated forms are called oncogenes. Oncogenes can lead to cancer.

You can’t completely prevent a mutation from happening in a proto-oncogene, but your lifestyle may have an impact. You may be able to lower your risk of cancer-causing mutations by:

Even with a healthy lifestyle, changes can still happen in a proto-oncogene. This is why researchers are currently looking into oncogenes as a major target for anticancer drugs.