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Genetic testing is a medical test that looks for changes in chromosomes, genes or proteins that are linked to cancer and other diseases. Genes that are linked to cancer are sometimes called cancer genes. Some genes and genetic changes are also linked to inherited conditions called family cancer syndromes, which increase the risk of cancer. These are sometimes called hereditary cancer syndromes or inherited cancer syndromes.
Your doctor may recommend genetic testing if they think you have a risk of developing cancer based on your personal or family history. Some cancers, such as breast, ovarian and colon, happen more often in some families than in others. Although genetic testing can help find links to disease, it only provides a piece of the information about a person’s health. Your risk of developing cancer may also be affected by other genetic factors or things around you, such as where you live, how you live your life, what you eat and how physically active you are.
It’s important for doctors to ask about your family’s health history regularly because this information helps identify patients who are most likely to benefit from genetic testing. Genetic testing can help families better understand their risk of cancer and other diseases. Depending on the situation, your doctor may suggest genetic testing for you or the family member with cancer. If a genetic test identifies an inherited gene mutation, other family members may also be offered genetic testing.
Benefits of genetic testing
Genetic tests have potential benefits, whether the results are positive or negative. Getting tested may:
- help you better understand your risk of cancer
- relieve your anxiety or uncertainty about cancer risk
- help you make decisions about your health and learn ways to help lower your risk of cancer
- help other family members decide if they should get tested or learn about how to lower their risk of cancer
- lead to finding cancer earlier when treatment is most likely to work better
For example, your doctor may recommend that you have other medical tests or procedures to look for cancer if you test positive for a gene mutation. If a screening test is available, they may also recommend that you start screening at an earlier age or get screened more often.
Drawbacks of genetic testing
Genetic testing may also have drawbacks that you should think about before you have the test:
- If you test positive for a genetic change linked to cancer, it doesn’t mean that you will develop cancer.
- If you test negative for a genetic change linked to cancer, it doesn’t mean that you won’t develop cancer.
- Genetic tests can’t find all genetic changes linked to cancer. Researchers haven’t discovered all of the genetic links, and current tests only look for certain genetic changes.
- There may not be effective ways to prevent the type of cancer caused by a certain gene mutation.
- Not all family members want to know their risk of disease.
- Genetic test results can lead to more medical appointments, tests and procedures if you test positive for a gene mutation.
Who can have genetic testing?
Not everyone qualifies for genetic testing. Your doctor will look at your personal and family history to see if they should recommend that you have genetic testing. Some people also decide not to have genetic testing even if it’s recommended. It is your right to choose whether or not to have genetic testing.
Genetic testing in children is complicated. Experts often recommend that genetic testing isn’t done until age 18 or older unless the results of the test will affect the child or adolescent’s care. Even if a child or adolescent has a gene mutation or family cancer syndrome, they won’t usually develop cancer until they become an adult. Waiting until adulthood to be tested also allows them to make their own decision about genetic testing. But earlier genetic testing may be recommended if there is a risk of developing cancer during childhood.
What happens during genetic testing?
If genetic testing is recommended, you will have a genetic risk assessment and genetic counselling. You will also have to give your consent to have the test.
You will usually have a risk assessment by a doctor, nurse or genetic counsellor. A risk assessment will look at how likely you are to develop a certain disease, such as cancer, based on your family history and other factors. During a risk assessment you will be asked about:
- why you want to have genetic testing
- your family history including history of cancer, genetic conditions and birth defects
- your medical history
- your lifestyle factors such as diet, whether or not you smoke and whether or not you are physically active
- You may also have a physical exam during the risk assessment.
Most people will see a genetic counsellor, who will explain how cancers are inherited and how inheriting certain genetic changes can increase the risk of cancer. They will discuss the benefits and drawbacks of genetic testing and help answer any questions you have. They can explain how genetic testing may affect you and your family. They can also suggest which other family members may want to consider having a genetic test.
You will need to give your informed consent if you decide to have genetic testing after the risk assessment and genetic counselling. You will be given information about the test, how accurate the test is and the benefits and risks of having the test. You won’t have genetic testing unless you give your consent.
Having the genetic test
A genetic test looks at DNA in a sample of cells taken from the blood, tissue, skin or urine.
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.
Types of genetic tests
There are different types of genetic tests that look for changes in chromosomes, genes and proteins.
Molecular genetic tests
Molecular genetic tests look for changes or mutations in genes. Some molecular genetic tests look at only one gene (called single-gene tests) while other tests look for mutations in several genes at the same time (called panel tests). Molecular genetic tests are also used to diagnose family cancer syndromes. Molecular genetic tests also include tests that look for changes in chromosomes such as missing or extra copies and missing or rearranged parts of chromosomes.
Biochemical genetic tests
Biochemical genetic tests look at the structure and amount of proteins and enzymes in cells.
Direct-to-consumer (DTC) testing
Some companies have started marketing directly to the person who will be having the test and providing at-home genetic testing services. This is called direct-to-consumer (DTC) testing. With this service, the person pays for the genetic test themselves and a kit is sent in the mail instead of having to go through a healthcare professional. If you choose a DTC test, you may or may not be offered the chance to talk to a genetic counsellor, who provides support and information and discusses the benefits and drawbacks of genetic testing.
With a DTC test, you collect a DNA sample at home. This is often done by swabbing the inside of the cheek (called a buccal sample) and sending the sample to a lab. In some cases, the person goes to a lab to have their blood taken. The results of the DTC genetic test are given by mail or over the telephone. In some cases, a genetic counsellor or healthcare professional provides the results and answers questions.
More research is needed to understand the benefits and drawbacks associated with DTC testing. But if you decide to get it done, look for a company that:
- gives test results from a certified lab
- offers genetic counselling before and after testing
- protects your privacy and is confidential
- offers easy-to-understand information
The company should be able to tell you how accurate the test is and how well it predicts the risk of a specific disease or condition. They should also be able to tell you how to manage or prevent a condition related to a genetic change.
There are not a lot of laws about DTC genetic testing so you could receive different reports from different companies. This can be very confusing. You may also be worried about how your genetic information is used and shared and whether appropriate consent processes are in place.
Whole genome testing
It is now possible to analyze a person’s overall genetic makeup using whole genome testing. Researchers are trying to find out if whole genome testing can help prevent, predict or treat cancer. Whole genome testing is generally only available outside of the healthcare system and you have to pay for it yourself. Several companies outside Canada offer direct-to-consumer (DTC) whole genome testing. Whole genome testing is used for different purposes, including determining paternity (finding out who is the father of a child), ancestry, a person’s risk of disease, such as cancer, or a person’s response to a particular treatment.
Getting the test results
Your doctor or genetic counsellor will get a lab report with the results of your genetic test. It may take several weeks or months to get the results. Genetic test results aren’t always easy to understand. This is why it’s important that a doctor or genetic counsellor explains the test results. If your results show you have a genetic change linked to cancer, they can discuss ways to help manage your risk.
You may also wish to tell your family that you are being tested and talk to them before you get the results of your test. Some family members may want to know if they should also get tested if you have a genetic change linked to cancer. But other family members may not want to know their own risk.
A positive test result
A positive test result means that you have a change in a gene, chromosome or protein that may increase your risk of cancer. But there is no way to know for sure if you will develop cancer. Your doctor or genetic counsellor can help you make decisions about your health and what you can do to help lower your risk of cancer developing. This may include making changes to the way you live, having tests to look for cancer, getting screened more often or at a younger age, knowing the signs and symptoms of a certain type of cancer, taking medicines to lower the risk of cancer or in some cases having preventive (prophylactic) surgery to remove an organ where cancer could develop.
A negative test result
A negative test result means that you don’t have the genetic change that the test was looking for. But it doesn’t mean that you won’t develop cancer.
An inconclusive test result
An inconclusive test result means that the test can’t tell whether or not you have a certain genetic change. If you have an inconclusive test result, you may still have a higher risk of developing cancer.
Variants of unknown or uncertain significance (VUS)
Genetic testing may find a genetic change that isn’t currently known to be linked to cancer or other conditions. This is called a variant of unknown or uncertain significance (VUS). Some types of VUS are more common than others. More research will help scientists to better understand whether certain gene changes reported as VUS are indeed linked to cancer or other types of disease. Your doctor and genetic counsellor can help keep you up to date on research about gene changes classified as VUS. VUS may eventually be linked to a certain cancer or disease as more research on that specific genetic change becomes available.
deoxyribonucleic acid (DNA)
The molecules inside the cell that program genetic information. DNA determines the structure, function and behaviour of a cell.
A protein that speeds up certain chemical reactions in the body.
For example, enzymes in the intestines help to digest food.
All the genetic or hereditary material of an organism.
The human genome is made up of all the DNA in a person’s 23 pairs of chromosomes.