Family History

Genetics

What is family history and how does it affect my risk?

People who have “family medical histories” of colorectal cancer are more likely to develop the disease. That means more than one first-degree relative (parent, sibling or child) has had colorectal cancer or colorectal polyps. Risk increases if relatives were diagnosed at a young age. In some families, parents can pass along changes in certain genes that can lead to colorectal cancer in their children. Scientists have identified several “genetic mutations” for colorectal cancer, and there might be others that have yet to be found.

• Familial Adenomatous Polyposis (FAP), or its variation, Gardner’s syndrome, is a condition in which people develop hundreds or thousands of polyps in their colons during their childhood. Most often, cancer will develop in one or more of these polyps. The condition is easy to diagnose with colonoscopy. If the disease is found before the polyps have become cancerous, surgical removal of the colon can prevent colorectal cancer. People with family histories of FAP should talk with their health care professionals about starting screening at adolescence. If they have symptoms, such as rectal bleeding or unexplained weight loss, earlier screening may be needed. Genetic testing is available to determine if someone has inherited FAP.
• Hereditary Non-Polyposis Colorectal Cancer (HNPCC), also known as Lynch syndrome, forms at an early age and involves only a few polyps. People with strong family histories of colorectal cancer or people who know that their relatives carry the HNPCC gene should talk with their health care professionals about screening. It’s recommended that people at risk of this cancer get screened every one to two years starting at age 25 or 10 years younger than the earliest age in which it was discovered in their families, whichever comes first. The risk of other types of cancer, including cancers of the uterus, stomach, small intestine, urinary tract and ovaries, is much higher and seems to occur at an earlier age for people with HNPCC. Early testing for these cancers is strongly recommended.

In addition to these hereditary colon cancers, there are other genetic problems that are not cancers or precancerous conditions and also increase colorectal cancer risk. These include Peutz-Jeghers syndrome (which can cause dark freckles on the lips and mouth), Juvenile Polyposis and Cowden syndrome. People with a family history of colorectal polyps or colorectal cancer should talk with their health care professionals about genetic counseling and testing.

Genetic testing allows for improved diagnosis

Because scientists have identified the genes responsible for hereditary colon cancer syndromes, we now have genetic tests that can determine whether or not a person has inherited the mutation.

Genetic testing of people without colorectal cancer, but who have a family history of the disease, typically involves taking a small sample of blood. The testers take DNA from white blood cells in the sample and look for the mutations.

When health care professionals suspect colorectal cancer is the result of HNPCC, a sample of the tumor is examined to screen for genetic instability. If the genes are unstable, then a blood sample can be used to test for a mutation in one of the several genes that has been linked to HNPCC. This test is not always definitive. In more than 30 percent of families with HNPCC, a mutation can’t be detected by genetic testing.

When considering genetic testing for colorectal cancer, it is important to speak with a genetic counselor. Genetic counselors can help you understand what having a genetic test may mean and help you make a decision about whether testing is right for you.