Understanding Genetic Testing for Cancer Risk

For certain types of cancer, genetic tests are available to help you learn about your risk. Before deciding to get genetic testing, it's important to understand what these tests look for and what they can and cannot tell you about your cancer risk.

What is genetic testing?

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

Genetic testing can be used in many ways, but here we’ll focus on how it is used to look for gene changes that are linked to cancer. (To learn about the role of genes and how mutations can lead to cancer, see Genes and Cancer.)

Genetic testing to help evaluate cancer risk

Predictive genetic testing is a 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 suggested for:

• A person with a strong family history of certain types of cancer, to see if they carry a gene mutation that increases their risk. If they do have an inherited mutation, they might want to have screening tests to look for cancer early, or even take steps to try to lower their risk. An example is testing for changes in the BRCA1 and BRCA2 genes (which are known to increase the risk of breast cancer and some other cancers) in people with several family members who have had breast cancer.
• A person already diagnosed with cancer, especially if there are other factors to suggest the cancer might have been caused by an inherited mutation (such as a strong family history, if the cancer was diagnosed at a young age, or if the cancer is uncommon, such as breast cancer in a man). Genetic testing might show if the person has a higher risk of developing some other cancers. It can also help other family members decide if they want to be tested for the mutation.  
• Family members of a person known to have an inherited gene mutation that increases their risk of cancer. Testing can help them know if they need screening tests to look for cancer early, or if they should take steps to try to lower their risk.

Most people (even people with cancer) do not need this type of genetic testing. It’s usually done when family history suggests that a cancer may be inherited (see below) or if cancer is diagnosed at an uncommonly young age.

Who might benefit from genetic testing?

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 talking to a genetic counselor about genetic testing:

• Several first-degree relatives (mother, father, sisters, brothers, children) with cancer
• Many relatives on one side of the family who have had the same type of cancer
• A cluster of cancers in your family that are known to be linked to a single gene mutation (such as breast, ovarian, and pancreatic cancers, which are sometimes linked to BRCA gene mutations)
• A family member with more than 1 type of cancer 
• Family members who had cancer at a younger age than normal for that type of cancer
• Close relatives with cancers that are linked to rare hereditary cancer syndromes
• A rare cancer (in you or a family member), such as breast cancer in a man or retinoblastoma
• A particular race or ethnicity (such as Ashkenazi Jewish ancestry, which is linked to a higher risk of BRCA gene mutations)
• A physical finding that’s linked to an inherited cancer (such as having many colon polyps)
• A known genetic mutation in one or more family members who have already had genetic testing
• Lab tests of your cancer cells that show features that might be linked to an inherited gene mutation

If you are concerned about a pattern of cancer in your family, cancer you’ve 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.

For more information on the types of cancer that may be linked to inherited genes, see Family Cancer Syndromes.

What is genetic counseling?

Genetic counseling gives you information that you and your family can use to make decisions about whether to get genetic testing (see below).

Genetic counselors have special training in the field of genetic counseling. Most are board-certified, and some might have a license depending on the rules in their state. Some doctors, advanced practice oncology nurses, social workers, and other health professionals may also provide genetic counseling, although they might have different levels of training in this field. If you are offered genetic counseling, it’s fair to ask about their training in this area.

What does a genetic counselor do?

Before and after genetic testing, a genetic counselor can help you understand:

• Your risk of getting certain types of cancer based on your family's medical history
• What you can do about this risk
• Which genetic tests can give you more information about your risk level
• What your test results might mean
• The privacy of your genetic information

Your counselor will explain the testing process. They can tell you more about what the tests can and cannot do and how well they work. Together, you will also discuss how knowing the test results may affect your emotions, mental health, and family. This information can help you decide if having genetic testing is right for you. It is your decision to have testing and what steps you take after.

Before you get tested...

It’s important to find out how useful genetic testing might be for you before you do it. Talk to your health care provider and plan on getting genetic counseling before the actual test. This will help you know what to expect. Your counselor can also tell you about the risks and benefits of the test, what the results might mean, and what your options are. 

Your health care provider can refer you to a genetic counselor in your area, or you can find a list of certified genetic counselors on the website of the National Society of Genetic Counselors.

To learn more, see What Should I Know Before Getting Genetic Testing?

Testing cancer cells for gene changes

Sometimes after a person has been diagnosed with cancer, the doctor will order tests on a sample of cancer cells to look for certain gene or protein changes. These tests can sometimes give information on a person’s outlook (prognosis), and they might also help tell if certain types of treatment may be useful.

These types of tests look for acquired gene changes only in the cancer cells. 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 Biomarker Tests and Cancer Treatment. 

Home-based genetic tests

Some tests that look for gene changes can be bought without needing a doctor’s order. For this type of testing, you purchase a test kit and send a sample of your DNA (often from saliva) to a lab for testing.

If you are considering using a home-based genetic test (also known as a direct-to-consumer genetic test), you need to know what it’s testing for, what it can (and can’t) tell you, and how reliable the test is. Even if a test from a reputable company is able to give accurate results, there are still likely to be limitations on what it can tell you.  

Home-based tests do not provide information on a person’s overall risk of developing any type of cancer. Sometimes these tests can sound much more helpful and certain than they have been proven to be. It may sound like the test will provide an answer to your specific health concern, such as your risk of hereditary cancer, but the test may not be able to answer that question completely. For example, a test may look for mutations in a certain gene, but it might not test for all of the possible mutations. So a negative test result, even if accurate, may miss the bigger picture regarding your cancer risk and what you can do to manage it. And you might not be provided with the important context about the test results that a genetic counselor could provide.

Home-based genetic tests should not be used instead of cancer screening or genetic counseling that may be recommended by a medical professional based on your individual risk for cancer. Always consult with your doctor if you are considering or have questions about genetic testing. Trained genetic counselors can help you know what to expect from your test results.