Approximately 5% of all colon (large bowel) cancers
are directly caused by inherited genetic abnormalities. These
hereditary colon cancers often feature colonic polyps or growths
that eventually become cancerous. There are several kinds, including
familial adenomatous polyposis (FAP) and a variant called Gardner's
syndrome. Another type, hereditary non-polyposis colon cancer
(HNPCC), features few if any polyps. Relatively rare hereditary
conditions such as Peutz-Jeghers syndrome and juvenile polyposis
are not cancer or precancerous conditions but confer on the patient
a greater than normal risk of developing colon cancer. Many families
with higher than normal rates of colon cancer have one or more
of these conditions. While non-hereditary ("sporadic") colon cancer
rarely occurs before age 40, hereditary colon cancers often occur
in younger people.
Experts in hereditary colon cancers strongly
recommend that people with unusually high rates of colon cancers
in their families be surveyed regularly for cancerous growths,
even if they have no symptoms. Colonoscopy is the most effective
and most widely used method of surveillance for hereditary colon
cancers. In colonoscopy, a narrow flexible tube is inserted into
the colon through the rectum. At the end of the tube is a tiny
light and video camera which allows the physician to see the inside
of the colon.
Colonic polyps, or adenomas, are relatively easy to diagnose by
colonoscopy. FAP and Gardner's syndrome are characterized by hundreds,
even thousands, of polyps. If the disease is caught in the precancerous
stage, cancer can be prevented by removing the colon surgically.
If the disease has progressed to the cancerous stages, surgery
may or may not be an effective treatment. In families known to
carry a gene for one of these diseases, surveillance for polyps
should begin at age 10 to 12.
Although HNPCC usually does not feature the highly
conspicuous polyps, it too is best detected with colonoscopy.
One type, Lynch syndrome I, begins at a young age, is more likely
to be in the proximal (upper, or right) colon, and is often accompanied
by other colon tumors. Lynch syndrome II has all of these features
and is also often accompanied by cancers outside the colon, especially
in the endometrium (the lining of the uterus) and the ovaries.
HNPCC may also be associated with cancers of the stomach, small
bowel, pancreas, urinary tract, or larynx in some families. In
families known to be affected by HNPCC, regular surveillance with
colonoscopy should begin at about age 25.
Many clinics, hospitals, and cancer centers that
treat people with hereditary colon cancer maintain registries.
A registry is a list of families known to be affected by a particular
genetic disease. These lists help identify all the family members
who might carry the disease and should be surveyed. Registries
and regular surveillance help save lives by prevention and early
detection of hereditary colon cancers.