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

Relatives of people who have had colorectal cancer, and people who have a "family history" of the disease, are more likely to develop the disease themselves.

Parents can pass along to their children changes in certain genes that can lead to colorectal cancer. Scientists have identified several of these genetic mutations for colorectal cancer, but there might be others that have yet to be found.

• People with Familial Adenomatous Polyposis (FAP), or its variation, Gardner's Syndrome, develop hundreds or thousands of colonic polyps during their childhood. The condition is relatively easy to diagnose with colonoscopy, and if the disease is caught in its precancerous stage, surgical removal of the colon can prevent cancer. Those with family history of FAP should talk with their health care professional about starting screening at adolescence or sooner if symptoms such as rectal bleeding or unexplained weight loss develop. Genetic testing is available to determine if someone has inherited FAP.
• Hereditary Non-Polyposis Colorectal Cancer (HNPCC) forms at an early age and only involves a few polyps. People with strong family history of colorectal cancer or relatives of known HNPCC gene-carriers should talk with their health care professional about screening. It is recommended that those at risk of this cancer undergo screening every one to two starting at age 25 or 10 years younger than the earliest case in the family, 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 those with HNPCC. Early testing for these with pelvic exam, transvaginal ultrasound and upper GI endoscopy are strongly recommended, as well as ultrasound and urinary analysis to screen for urinary-tract and renal-cell cancers.

In addition to these hereditary colon cancers, there are other syndromes that are not cancers or precancerous conditions but carry a greater colorectal cancer risk. These can be identified by genetic testing and include Peutz-Jeghers syndrome (marked by dark freckles on the lips and mouth), Juvenile Polyposis and Cowden syndrome.

Genetic testing allows for improved diagnosis

Because scientists have identified the precise 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 (abnormalities).

When a colorectal cancer is suspected to result from HNPCC, a sample of the tumor is examined to first 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, however, since a mutation cannot be detected by genetic testing in more than 30 percent of families with HNPCC.

When considering genetic testing for colorectal cancer, it is important to seek genetic counseling. Genetic counselors can help you understand the implications of the test in terms of insurance, costs, discrimination and potential psychological benefit or distress.