Doctors generally do not rely on genetic testing to screen for, or make an initial diagnosis of, colorectal cancer. However, under some circumstances genetic testing is appropriate. It may be offered to high-risk families to determine an individual's risk for developing certain genetic forms of colorectal cancer.
For example, there is a test that can be used to detect the variant APC gene (a variation of the APC gene), which predisposes some people to developing familial adenomatous polyposis. This test, which is performed on a small sample of blood, does not rule out mutations that cause other forms of hereditary colon cancer.
Lynch syndrome is a genetic condition that makes people more likely to develop certain cancers. People who have it also have about a 50% to 80% chance of getting colorectal cancer by age 70. They’re also at risk for cancers of the uterus, ovaries, and stomach. And they tend to get cancer at younger ages than other people, often in their 30s and 40s.
Lynch syndrome is sometimes called hereditary non-polyposis colorectal cancer (HNPCC), Muir-Torre syndrome, and Turcot syndrome.
Any person of Ashkenazi Jewish descent may consider genetic counseling and testing if there is a personal or family history of colon cancer or pre-cancerous polyps. People of Ashkenazi Jewish descent without a family history of colorectal cancer may want to consider genetic counseling to determine the value of testing, given their circumstances.
How Should I Interpret the Results of Genetic Testing?
A positive test result means that you have an increased risk of developing colorectal cancer in your lifetime. If you already have had colon cancer or polyps, it may affect screening recommendations. This test does not detect the presence of cancer or polyps.
If you test negative for this gene variant, it means that you do not have this specific cancer risk. But, you may still have a mutation in another gene that causes hereditary colon cancer. Risk may be evaluated through genetic counseling, where family history, lifestyle, and other issues may be discussed.
What Should I Do if I Test Positive for the APC Gene Variant?
Early diagnosis is important for preventing colorectal cancer. At this time, experts have made the following recommendations for people who test positive for the APC gene variant:
People with a positive gene test should have a routine colonoscopy every year, beginning at puberty.
People with a personal history of coloncancer or polyps should consider a colectomy.
Relatives of people testing positive for this gene mutation should consider genetic counseling and testing.
Note: These recommendations may be subject to change, based on specific family history information. It is important to talk with your doctor to determine the most appropriate screening practice for you.