Overview

Colorectal cancer genetic testing can tell you if you carry rare changed, or mutated, genes that can cause colorectal cancer. Although most people who get colorectal cancer do not have one of these mutated genes, having certain gene changes can increase your chance of getting colorectal cancer.

The most common genetic changes related to colorectal cancer are familial adenomatous polyposis (FAP) and Lynch syndrome. In these conditions, screening often starts sooner than age 40.

Your doctor may suggest genetic testing if your family history or your personal medical history puts you at an increased risk for colorectal cancer. If you have an increased risk, your doctor may also recommend you start cancer screening earlier than someone who has an average risk of cancer.

What the Results Mean

A positive result means that you may have one of the changed genes that causes familial adenomatous polyposis (FAP) or Lynch syndrome. It also means that you have a much higher risk of getting colorectal cancer (and maybe other cancers).

If you have a positive result, you will be able to take action that may help you and your family members live longer. This includes starting screening at a younger age and having screening tests more often.

A negative result means that none of these genes were found in your blood sample.

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Accuracy of the Test

Although these genetic tests are highly reliable, no test is 100% accurate. Depending on the type of test you have, you can find out if you have certain inherited gene changes. These changes may be related to some of the common syndromes that increase your risk for colorectal cancer, such as Lynch syndrome. But the tests cannot tell you when or if you will develop colorectal cancer.

Deciding About Testing

The decision to have genetic testing for colorectal cancer is personal. You may have emotional, financial, and family reasons for taking or not taking the test. You might want to be tested so that if you test positive, you can be proactive with cancer screening and take measures to protect your health and that of your family. Or you may be concerned that if you test positive, you may have a hard time getting life insurance, long-term care insurance, or disability insurance. In Canada, there is a law called the Genetic Non-Discrimination Act (GNA). It protects your genetic information.

Genetic counselling can help you understand the risks and benefits of testing and help you make a well-informed decision.

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Genetic Counselling

The results of genetic testing can affect your life. It may be a good idea to get genetic counselling before deciding to have testing. Genetic counsellors can explain the pros and cons of testing, but you make the decision about whether to have the test. A genetic counsellor can help you make well-informed decisions. Genetic counselling can help you and your family:

• Understand medical facts about a disease and what you may be able to do to manage it.
• Understand how your family history contributes to the development of a disease.
• Explain the results of a genetic test.
• Help you find resources, including getting referrals to specialists or finding local support groups.

Genetic counsellors have specialized training in medical genetics and counselling. They are sensitive to the physical and emotional aspects of these decisions. Your privacy and confidentiality are carefully protected.