Genetic testing uses special tests to identify people with an increased risk for cancer. Genetic testing may be considered if your healthcare team suspects you may have a genetic risk for cancer based on your personal history or family history.

Genetic tests find changes (mutations) to a gene, or a number of genes on a chromosome, that are associated with some inherited disorders or cancers. Genetic tests are available for people who may have an increased risk of certain cancers, such as breast, ovarian and colon cancer. These cancers occur more often in some families than in others. Genetic testing only provides a piece of information about a persons health. Other genetic and environmental factors and lifestyle choices affect a persons risk of developing cancer.

Genetic education and counselling is done before genetic testing. These resources help you make informed decisions and adapt to and manage possible risks.

Genetic tests have potential benefits, whether the results are positive or negative.

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Genetic testing has some limits.

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Not everyone qualifies for genetic testing. A person may not be offered genetic testing for several reasons. These reasons are discussed at the genetic counselling session.

Some people decide not to have genetic testing when they understand the implications of testing. It is their right to choose whether or not they go ahead with testing.

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Genetic testing involves examining a persons DNA. A sample of blood, skin or tissue is usually taken from a family member who has had cancer. The test searches for the defect or mutation known to be associated with the type of hereditary cancer in question. If the mutation is found, other family members can be tested, usually by doing a blood test.

Sometimes the healthcare team will do a physical examination to check if you have physical signs that suggest a hereditary cancer syndrome or to rule out an existing cancer.

If there is no close, living, affected relative who can be tested, testing can sometimes be done on stored tissue or DNA of a deceased relative. Testing stored tissue is technically difficult and may not give a conclusive result. If a living affected relative declines testing, other options may be discussed and an unaffected person may be tested. In these cases, the result is often uninformative because a negative result does not rule out the presence of a cancer susceptibility gene in the family or the person being tested.

Genetic testing should always be done at a clinic that provides supportive counselling and education. However, some companies have started marketing direct-to-consumer (DTC) or at-home genetic testing services. With this service, the consumer usually buys the genetic test themselves instead of having to go through a healthcare professional. The consumer collects the DNA sample at home, often by swabbing the inside of the cheek (called a buccal sample), and sends it back to the laboratory. Sometimes the customer has to go to a laboratory to have blood taken. The consumer is notified of the results by mail or telephone. In some cases, a genetic counsellor or healthcare professional provides the results and answers questions. DTC gives a consumer access to genetic information without going through a doctor or insurance company. DTC genetic testing varies in price and can be very costly. DTC genetic tests have significant risks and limitations.

The medical community has many concerns about DTC genetic testing and about ensuring regulations are in place so that the consumer:

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There may be a fee for genetic testing. Provincial, territorial or personal health insurance plans may cover the fee if the test is ordered by a doctor. It may also be covered if it is part of a research study. Make sure you ask about fees before being tested. The cost for genetic testing varies depending on how complex the test is.

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Genetic testing is complex, so it is important to have a trained professional explain the results. It can also take several weeks or months to get the results of the test.

Genetic testing is usually done in a family member with cancer who has a family history that suggests a particular hereditary cancer syndrome. Testing in someone who already has cancer can have 3 possible results:

Predictive genetic testing looks for a known inherited cancer susceptibility mutation in a person who does not have cancer. This type of genetic testing helps identify whether a person is carrying a gene mutation that puts them at an increased risk of developing cancer. There are 2 possible results with predictive genetic testing:

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There are special considerations when doing genetic risk assessment and genetic testing for mutations in children. Genetic testing in children is very complex.

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Read this article:
Genetic testing - Canadian Cancer Society

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