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Untitled Document
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| FAP |
| What Is FAP? |
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By
Miriam Komaromy,
MD
Reviewed
by Peggy Conrad,
MS, CGC and Jonathan
Terdiman, MD
Last updated August 1, 2000
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Familial
adenomatous polyposis, or FAP, describes an inherited
medical syndrome that puts affected individuals at enormous
risk for the early development of colon cancer unless
they take preventive action.
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What
Is FAP?
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all people with FAP will develop colon cancer if
they do not get treatment. |
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FAP
occurs when a person is born with a mutation in a specific
gene called the adenomatous polyposis coli (APC) gene.
People born with FAP are at nearly 100 percent risk of
developing colon cancer if they do not undergo surgery.
They also have an elevated risk of contracting certain
other types of cancer. Among them are cancer of the small
bowel (the part of the digestive tract located above the
colon and rectum); cancer of the thyroid and cancer of
the brain, as well as a rare form of childhood liver cancer.
People with FAP account for roughly one percent of all
colon cancer cases. About 1 in every 8,000 people has
FAP. |
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How Does FAP Cause Colon Cancer?
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The
colon illustrated above is riddled with polyps,
which is typical in FAP patients.
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Typically,
individuals with FAP begin developing polyps, or small
mushroom-like growths, in their colon and rectum by their
teenage years. However, some may start developing these
polyps much earlier, as children.
Polyps
are believed to be the first stage in nearly all cases
of colon cancer, not just those that occur in FAP. The
difference in FAP is the quantity and early appearance
of these growths. Unlike others diagnosed with colon cancer,
who typically have fewer than ten polyps and usually do
not begin developing them
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What
Determines an FAP Diagnosis?
A finding of more than 100 adenomatous polyps in
a patient's colon or rectum,
OR
A finding of less than 100 adenomatous polyps in
the colon or rectum of a patient who has a relative
who has been diagnosed with FAP. |
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until they're
in their 50s, FAP patients will develop hundreds
or even thousands
of polyps much earlier in their lives. Once these polyps
begin to appear, some will almost always become
cancerous if left untreated. As a result, individuals
with FAP tend to develop colon cancer much earlier than
the general population: at an average age of 39, as opposed
to 65.
A
rare related syndrome called attenuated
FAP (AFAP), is sometimes diagnosed when patients have
less than 100 polyps. Although patients with AFAP are
still strongly predisposed to colon cancer, they tend
not to get diagnosed with cancer until about a decade
later than those who have "classic" FAP. It's
important to note, however, that these are averages, and
cancerous polyps often develop at much earlier ages —
even in childhood. |
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Family
Medical History
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Polyps
in the colon and rectum rarely produce symptoms. And because
most people aren't routinely screened for colon cancer
until they're in their 50s, polyps can easily go undetected
in younger people. As a result, doctors must rely on clues
from a patient's family medical history to diagnose the
syndrome in time to make a difference. For example, when
other family members
have been diagnosed with the FAP syndrome, or have developed
colon cancer at an unusually early age.
Colon
Cancer:
Average Age of Onset
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FAP is inherited in what's called autosomal
dominant fashion. This means that a person only needs
to inherit one mutated version of an FAP associated gene
in order to have FAP and a high risk for cancer. Because
of the way we inherit genes, if one of your parents has
FAP, you have a 50 percent chance of inheriting it. Likewise,
if you have FAP, your children have a 50 percent chance
of inheriting it. |
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Screening
and Prevention
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In
families with a history of FAP, screening
for polyps should begin between age 10 and 12, and be
repeated every year until polyps appear. Once polyps
appear, removal of the colon is usually recommended
because of the near inevitability of developing colon
cancer, though this may be put off for several years
if the polyps are still very small.
If there has been a lot of colon cancer or colon polyps
in your family,
or colon cancer has been diagnosed at an unusually early
age in close relatives,
you
should:
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- Analyze
your family
medical history with a genetics specialist to
determine if you might have FAP.
- Have
a doctor examine you for certain physical features
that provide clues which suggest that you may have
FAP.
- Consider
genetic testing for mutations in the APC gene to determine
which family members have inherited FAP, although
this is not usually the first step in making the diagnosis
of FAP in a family.
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References
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Bertario,
L. et al. (1997). Recommendations for clinical management
of familial adenomatous polyposis. Tumori 83:
800-803.
Jarvinen, H. (1992). Epidemiology of familiial adenomatous
polyposis in Finland: inpact of screening on colorectal
cancer rate and suvival. Gut 33: 357-360.
Ivanovich, J. et al. (1999). A practical approach to
familial and hereditary colorectal cancer. Excerpta
Medica 107: 68-77.
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