Colon cancer genetic testing is a blood test that can tell you
whether you carry rare changed, or mutated,
genes that can cause
colon cancer. Although most people who get colon
cancer do not have one of these mutated genes, having them greatly increases
your chance of getting colon cancer.
Colon cancer develops in the
large intestine when cells change and grow out of control. Colon cancer is
also called colorectal cancer, because it can occur in both the colon and in the
lowest section of the colon, which is called the rectum.
cancer almost always begins as small growths on the inner wall of the colon
polyps. A doctor can find and remove polyps during a
colonoscopy, a test in which a doctor uses a flexible
video camera or scope to look at the inside of the colon. If a close member of
your family, such as your brother, sister, or parent, has had colon cancer,
talk with your doctor about colonoscopy screening.
The most common
genetic changes related to colon cancer are familial adenomatous polyposis
(FAP) and hereditary nonpolyposis colorectal cancer (HNPCC). In these
conditions, screening often starts even sooner than age 40.
Familial adenomatous polyposis (FAP)
FAP develops because of a changed gene that causes
hundreds or thousands of polyps to grow in the colon. The number of polyps
increases with age. If one of your parents has FAP, you have a 50% chance of
having the changed gene and the disease.
Everyone who has FAP will get colorectal cancer if they are not treated. They can develop polyps in their
20s and 30s, or even earlier. People who have FAP need to have their colons
removed to prevent colon cancer.
Hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome
HNPCC can cause polyps in the colon, but not as many
as FAP. Changes in any of one or more different genes can cause HNPCC. These
changes also increase the risk of getting other cancers, including cancer of the
endometrium, ovaries, stomach, urinary tract, small intestine, skin, brain, and liver.
Having the gene change related to HNPCC does not mean
you definitely will develop colon cancer. But it does increase your chances of getting colon cancer at a younger age. And the cancer is more likely to grow faster. It also increases your chances of other cancers, so screening for endometrial or other cancers may be important. If a person has an HNPCC gene change, he or she has a 50% chance of passing this gene on to a child.