Genetic Testing for Colon Cancer

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Genetic counselor Meg Sheehan

Genetic counselor Meg Sheehan provides counseling to people who have an inherited risk of colon cancer.

If your doctor finds multiple polyps during a colonoscopy, it may be a sign that you have a hereditary syndrome that increases your risk of developing colon cancer. About 5 to 10 percent of colon cancer is due to changes in the genes that may be passed from parents to children. Our Clinical Genetics Service offers counseling and education about the risk of hereditary forms of colon cancer, as well as genetic testing for you and your family members.

During genetic testing, we may take a sample of tissue from your blood, a polyp, or a tumor (if you already have colon cancer). We’ll look at the sample for changes in your genes that are associated with hereditary syndromes that cause colon cancer. If we discover a mutation, your care team will determine which condition you have. Knowing about genetic changes can affect your treatment.

Doctors’ knowledge of genetic mutations continues to increase rapidly. Sometimes we may find a mutation that we don’t yet understand but that still might put you at a higher risk of hereditary cancer. If this happens, our counselors may recommend that you and your family members have screening more often.

Genetic Causes of Colon Cancer

Lynch Syndrome
Lynch syndrome (formerly known as hereditary nonpolyposis colorectal cancer) is associated with an increased risk of colon and rectal cancer, as well as endometrial, ovarian, gastric, urinary tract, brain, and pancreatic cancers. Lynch syndrome is the most common form of hereditary colon cancer. It is responsible for about 3 percent of all colon and rectal cancer.

Familial Adenomatous Polyposis
Familial adenomatous polyposis (FAP) consists of many precancerous polyps — possibly hundreds or thousands — in the colon and rectum. In a milder form of FAP, there may be a smaller number of polyps.

MYH-Associated Polyposis
MYH-associated polyposis is marked by multiple precancerous polyps in the colon and rectum, similar in number to that seen in the milder form of FAP. 

Hyperplastic Polyposis Syndrome
In hyperplastic polyposis syndrome (HPS), multiple hyperplastic polyps develop in the colon and rectum. Currently, there is no gene mutation known to be associated with HPS.