What about genetic testing for colon cancer?
Genetic testing using blood tests are now available to identify patients with hereditary colon cancer syndromes. Hereditary colon cancer syndromes are caused by specific inherited mutations that are sufficient in themselves to cause colon polyps, colon cancers, and non-colonic cancers. Hereditary colon cancer syndrome can affect multiple members of a family. Approximately 5% of all colon cancers in the US are due to hereditary colon cancer syndromes. Patients who have inherited one of these syndromes have an extremely high risk for developing colon cancer, approaching 90%
to 100%. Fortunately, blood tests are now available to test for these hereditary colon cancer syndromes, once a syndrome has been suspected within a family.
Familial adenomatous polyposis (FAP)
Familial adenomatous polyposis or FAP is a hereditary colon cancer syndrome in which the affected family members develop large numbers (hundreds, sometimes thousands) of colon polyps starting in their teens. Unless the condition is detected and treated early (treatment involves removal of the colon), a family member with the FAP syndrome is almost sure to develop colon cancer. Cancers most commonly begin to appear when patients are in their 40's, but can appear earlier. These patients also are at risk of developing other cancers such as cancers of the thyroid gland, stomach, and the ampulla (the part of the duodenum into which the bile ducts drain).
Attenuated familial adenomatous polyposis (AFAP)
Attenuated familial adenomatous polyposis or AFAP is a milder version of FAP. Affected patients develop less than 100 colon polyps. Nevertheless, they are at high risk of developing colon cancers at a young age. They are also at risk for stomach and duodenal polyps.
Hereditary nonpolyposis colon cancer (HNPCC)
Hereditary nonpolyposis colon cancer, or HNPCC, is a hereditary cancer syndrome in which affected family members tend to develop colon cancers, usually in the right colon, in their 30's to 40's. Certain HNPCC patients also are at elevated risk for developing uterine cancer, stomach cancer, ovarian cancer, cancers of the ureters (the tubes that connect the kidneys to the bladder), cancers of the bile ducts (the ducts that drain bile from the liver to the intestines), and cancer of the brain and skin.
MYH polyposis syndrome
The MYH polyposis syndrome is a recently discovered hereditary colon cancer syndrome. Affected patients typically develop 10-100 polyps during their 40's and are at high risk for developing colon cancer. The MYH syndrome is inherited in an autosomal recessive manner with each parent contributing one copy of the mutant gene.
This results in one chance in four that their offspring may inherit both copies
of the gene. Most people with the MYH syndrome do not have a multigenerational family history of polyps or cancer of the colon but may have brothers or sisters with it.