Genetic Testing for Colorectal Cancer

Genetic Testing

About 5-10% of colorectal cancer cases can be attributed to hereditary or inherited factors passed down from parent to child. This means that a small percentage of people are born with certain genetic mutations that make it more likely for them to develop colorectal cancer in their lifetime.

20-25% of cases are considered familial, which means that more family members may be affected than would be expected by chance alone, but a single genetic cause or explanation is not known.

70-75% of colorectal cancer cases can be attributed to sporadic gene mutations. This means that the gene mutations that cause the cancer to occur were acquired during the person’s lifetime, occurring only in the tumour cells, and not inherited from their parents.

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What is Genetic Testing?

Genetic testing is a type of medical test that closely examines a person’s DNA or genetic information to look for any changes or mutations that are linked to known diseases. It is typically done by analyzing the DNA present in a blood sample.

Genetic testing is voluntary, meaning that you decide if you want to participate or not. A geneticist or genetic counselor can help you by providing information about the pros and cons of the test and discuss any social and emotional aspects of testing.

Knowing your family health history is important. If there is a strong history of colorectal cancer or if one of your family members has a hereditary cancer syndrome like Lynch syndrome, be sure to talk to your doctor about genetic testing. Studies show that conversations between patients and their healthcare provider is the strong driver of screening participation.

You can download our Colorectal Cancer Family History Chart to better understand your family history of the disease.

Who Can Have Genetic Testing?

Not everyone qualifies for genetic testing. By examining your personal and family history, your doctor will see if genetic testing is right for you. Remember that genetic testing does not happen without genetic counseling and informed consent of each individual getting tested.

For More Information About Genetic Testing in Canada:

Benefits of Genetic Testing for Colorectal Cancer

While no one wants to find out that they have an inherited genetic mutation that could lead to cancer, knowing can help to control your risk.

  • Early colorectal cancer surveillance and risk reduction: A positive test result that indicates the presence of Lynch syndrome mutations can lead to appropriate risk reduction for affected individuals and their family members.

  • Early colorectal cancer detection: Genetic testing can also help to better explain the history of cancer in a family. When detected early, colorectal cancer has a 90% cure rate. By participating in genetic testing, positive health behaviours can be reinforced and cancer can be caught early when it is more treatable.

Limitations of Genetic Testing

Although genetic testing can provide important information about your health, there are several limitations to how useful this information can be. Consider the following before getting tested:

  • If you test positive for a mutation that is linked to cancer, it does not necessarily mean that you will develop cancer

  • If you test negative for a mutation that is linked to cancer, it doesn’t mean that you will not develop cancer
  • The current genetic tests that are available only look for certain mutations, meaning that some mutations that can cause cancer may not be detected
  • Not all family members want to know their risk of disease
  • Results may increase anxiety in some people
  • Genetic test results can lead to more medical appointments, tests and procedures if you do test positive for a gene mutation