Genetics, gene mutations, and cancer risk

Genetics is the field of science that looks at how traits (such as eye color) are passed down from parents to their children through genes.

Genes are pieces of DNA (deoxyribonucleic acid) inside our cells that tell the cell how to make the proteins the body needs to function. DNA is the genetic blueprint in each cell. Genes affect inherited traits passed on from a parent to a child, such as hair color, eye color, and height. They can also affect whether a person is likely to develop certain diseases, such as cancer.

Changes in genes, called mutations, play an important role in the development of cancer. Mutations can cause a cell to make (or not make) proteins that affect how the cell grows and divides into new cells. Certain mutations can cause cells to grow out of control, which can lead to cancer. Still, only about 5% to 10% of all cancers are thought to be strongly related to an inherited gene mutation.

Usually several gene changes or mutations are needed before a cell becomes cancer.

Most cancers start because of acquired gene mutations that happen during a persons lifetime. Sometimes these gene changes have an outside cause, such as exposure to sunlight or tobacco. But gene mutations can also be random events that sometimes happen inside a cell, without a clear cause.

Acquired mutations only affect the cells that grow from the mutated cell. They do not affect all the cells in the persons body. This means all the cancer cells will have the mutations, but normal cells in the body will not. Because of this, the mutations are not passed on to a persons children.This is very different from inherited mutations, which are in every cell in the body even the cells without cancer.

Genetic testing is the use of medical tests to look for certain mutations in a persons genes. Many types of genetic tests are used today, and more are being developed.

Genetic testing can be used in many ways, but here well focus on its use in looking for gene changes linked to cancer.

Predictive genetic testing is the type of testing used to look for inherited gene mutations that might put a person at higher risk of getting certain kinds of cancer. This type of testing might be advised:

Most people (even people with cancer) do not need this type of genetic testing. Its usually done when family history suggests theres a cancer that may be inherited (see below).

Sometimes after a person has been diagnosed with cancer, the doctor will do tests on a sample of cancer cells to look for certain gene changes. These tests can sometimes give information on a persons outlook (prognosis) and help tell whether certain types of treatment might be useful.

These types of tests look for acquired gene changes only in the cancer cells that are taken from the patient. These tests are not the same as the tests used to find out about inherited cancer risk.

For more about this kind of testing and its use in cancer treatment, see our information on specific types of cancer.

Genetic counseling and testing may be recommended for people who have had certain cancers or certain patterns of cancer

in their family. If you have any of the following, you might consider genetic testing:

If you are concerned about a pattern of cancer in your family, cancer youve had in the past, or other cancer risk factors, you may want to talk to a health care provider about whether genetic counseling and testing might be a good option for you.

You need to know your family history and what kinds of tests are available. For some types of cancer, no known mutations have been linked to an increased risk. Other cancer types may have known mutations, but theres no way to test for them yet.

Family Cancer Syndromes gives you more information on the types of cancers that may be linked to inherited genes.

Its important to find out how useful testing may be for you before you do it. Talk to your health care provider and plan to meet with a genetic counselor before the actual test. This will help you know what to expect. The counselor can tell you about the pros and cons of the test, what the results might mean, and what your options are.

More:
Understanding Genetic Testing for Cancer

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