Colon Cancer Prevention (cont.)
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%-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 syndrom. 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. 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.
Next: Who should consider genetic counseling and
testing? »
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- Colon Cancer Screening - Colon cancer screening include colonoscopy, fecal occult blood tests, flexible sigmoidoscopy, virtual colonoscopy, and air contrast barium enema.
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