Causes of Cancer

Cancer is caused by changes (mutations) to the DNA within cells. The DNA inside a cell contains a set of instructions telling the cell how to grow and divide. Errors in the instructions may allow a cell to become cancerous.

What do gene mutations do?

A gene mutation can instruct a healthy cell to:

Allow rapid growth. A gene mutation can tell a cell to grow and divide more rapidly. This creates many new cells that all have that same mutation.
Fail to stop uncontrolled cell growth. Normal cells contain genes called tumor suppressor genes that recognize out-of-control growth and act to stop it. But if a mutation occurs in a tumor suppressor gene, that gene may become less effective or may be turned off completely. This allows a mutated cell to continue growing and dividing.

Make mistakes when repairing DNA errors. DNA repair genes identify and correct DNA mutations. A mutation in a DNA repair gene means that the gene may miss some DNA errors. This allows more DNA mutations to occur and may lead to cancer.

These mutations are the most common ones found in cancer. But many other gene mutations can contribute to causing cancer.

What causes gene mutations?

Sometimes you're born with a genetic mutation. Or a genetic mutation can be caused by forces within your body, such as hormones, viruses and chronic inflammation. Genetic mutations can also be caused by forces outside of your body, such as ultraviolet (UV) light from the sun, cancer-causing chemicals (carcinogens) or radiation.

How do gene mutations interact with each other?

Researchers believe that more than one gene mutation is necessary to cause most cancers. Some blood cancers may require just one gene mutation to drive their growth. Most cancers that form in the body's major organs, such as the lungs and the colon, have many gene mutations. It's not clear just how many mutations must accumulate for cancer to form. It's likely that this varies among cancer types.

The gene mutations you're born with and those that you acquire throughout your life work together to cause cancer. For instance, if you've inherited a genetic mutation that predisposes you to cancer, that doesn't mean you're certain to get cancer. Instead, you may need one or more other gene mutations to cause cancer. Your inherited gene mutation could make you more likely than other people to develop cancer when exposed to a certain cancer-causing substance. The genetic mutation begins the cancer process, and the cancer-causing substance could play a role in further cancer development.