The American Cancer Society (ACS) estimates that there will be 106,100 new cases of colon cancer in the United States in 2009. Information about colon cancer is often grouped with information about rectal cancer. The colon and the rectum are different sections of the large intestine. Together, these cancers are called colorectal cancer. While the death rate for colorectal cancer has been dropping for 20 years, the ACS still expects it to cause 49,920 deaths in 2009.
Significance
Genetic testing for colon cancer aims to identify the people who are at greater-than-average risk for developing colon cancer. Some people have an inherited genetic mutation that increases their risk of developing colon cancer. If a genetic test determines that an individual has a genetic mutation that indicates increased risk, the person can be carefully monitored for the development of colon cancer. The National Cancer Institute (NCI) notes that, for colorectal cancer, "early detection of the disease greatly improves the chances of a cure."
Types
Researchers have identified several genes that can be linked to two types of colon cancer: FAP (familial adenomatous polyposis) and HNPCC (hereditary nonpolyposis colon cancer). A person with the FAP genetic condition has a greater than 90 percent chance of eventually developing colorectal cancer. A person with the HNPCC genetic condition has about a 70 percent chance of eventually developing colorectal cancer. Typically, these two types of cancer occur at a younger age than the nonhereditary varieties of colon cancer. A blood test is used to test for these genetic conditions.
Considerations
Genetic testing does not test for the presence of colon cancer. It tests for a genetic mutation that indicates that a person has a higher-than-average risk for colon cancer. Other tests, such as a colonoscopy, screen for signs of cancer. For people with no identifiable risk factors, the ACS recommends that routine screening begin at age 50. People who have the FAP or HNPCC genetic mutation should begin screening at a younger age. Genetic testing for colon cancer is not recommended for the general population. People who have a family history of close relatives with colon or rectal cancer should consider genetic testing.
Misconceptions
Most colon cancers are not associated with a known genetic condition. Together, FAP and HNPCC only account for approximately 5 percent of all colorectal cancers. As research continues, additional links between genes and colon cancer may be determined. People with no family history of colon cancer are susceptible to the disease and should follow screening recommendations.
Warning
There are risks associated with genetic testing. A positive test result can cause a great deal of stress and anxiety. Ideally, an individual will thoroughly discuss the pros and cons of genetic testing with a genetic counselor before testing. A negative test result cannot guarantee that a person does not have a genetic mutation--testing for FAP and HNPCC is not foolproof.
