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 person’s health. Other genetic and environmental factors and lifestyle choices affect a person’s 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.
- Knowing the results of genetic testing gives some people a sense of relief from uncertainty and helps them make informed decisions about managing their health.
- Genetic testing for a hereditary cancer helps identify people at high genetic risk for cancer. Once identified, the healthcare team can closely follow people and suggest measures to help prevent cancer. If you have genetic testing, you need to be fully informed about what is involved and understand the benefits and risks.
- Genetic testing is most useful when it is done in a family member with cancer who also has a family history that suggests a particular hereditary cancer syndrome. If testing identifies an inherited gene mutation in the affected family member, other family members may be offered genetic testing for that specific gene mutation. In this case, genetic testing can help clarify cancer risk in family members and determine whether they are at an average or higher risk for developing a particular type of cancer.
- Genetic testing has the potential to give you or your family personalized ways to prevent, screen for or treat a cancer based on information about a person’s genes. This approach is called personalized medicine. Researchers continue to find more genes that put people at a higher risk for developing cancer. It is now possible to analyze much of a person’s overall genetic make-up using whole genomegenomeAll the genetic or hereditary material of an organism. testing. This type of personalized medicine does not take family history or other risk factors for cancer into account, so the results should be interpreted carefully. The science of genomics (the study of the genome) is still new and is not a standard practice in medicine.
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Limits of genetic testing
Genetic testing has some limits.
- The tests may not find every mutation associated with a particular cancer. Some cancer genes have not been discovered yet, or the person can have a mutation that current testing cannot find.
- There may not be effective ways to prevent or treat the condition or cancer that is detected.
- Knowing that you are at risk for developing a disease sometime in the future can affect you emotionally and psychologically. Because genetic tests reveal information about you and your family, the test results can affect relationships in your family.
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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 person’s 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:
- receives results from an accredited laboratory
- receives and discusses the results with a qualified medical professional
- is assured privacy and confidentiality
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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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What the results mean
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:
- mutation detected – This result confirms that there is a gene mutation associated with a specific hereditary cancer syndrome. It provides an explanation for some of the cancers in the family.
- If genetic testing identifies an inherited gene mutation in an affected family member, targeted genetic testing for that specific gene mutation can be offered to other relatives. In this case, genetic testing can help clarify cancer risk in family members and determine if they are at an average or higher risk for developing a particular type of cancer.
- no mutation detected – This result means it is less likely that a specific hereditary cancer syndrome is present, but does not rule it out completely. This is called an uninformative result because it does not give an explanation for the cancer. The cancer may be hereditary but due to an undetectable gene mutation, or the cancer may not be hereditary. Genetic testing is only available for certain cancer genes.
- unclassified variant detected – This result means that there are changes in genes that are not currently well understood. These changes may or may not have any impact on risk of cancer.
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:
- A positive predictive test result means that a person inherited the known cancer susceptibility gene mutation in their family and is at increased risk of cancer. Although a positive result provides information about personal risk of developing cancer, it cannot tell if cancer will actually develop or when.
- A negative predictive test result means that a person did not inherit the known cancer susceptibility mutation in their family and is not at increased risk for cancers associated with the mutation. However, it doesn’t mean that the person will not get cancer.
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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.
- Experts often recommend that genetic testing be deferred until legal adult age (usually age 18 years or older), unless the results of genetic testing will impact the medical management of the child or adolescent. This recommendation is based on the potential discrimination and possible emotional effects that could result from genetic testing. Waiting until children reach adulthood also allows them to make their own decision about genetic testing.
- Genetic testing in a child should take into account the risk of cancer during childhood, as well as the evidence associated with reducing risk for the cancer.
- Some hereditary cancer syndromes increase a child’s risk for developing cancer. Effective screening or preventive strategies for these cancers can be done during childhood. Genetic testing may be offered for these syndromes.
- Genetic testing would likely not be offered when no risk reduction strategies are available for a child and the chance of developing a cancer during childhood is very low.
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