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Colon Cancer
• The life time risk of developing Colon Cancer in the United States in
one in sixteen.
• This means 144,000 new cases a year accounting for 9% of all
cancers.
• 10% of colon cancers have a genetic background.
• The risk for developing colon cancer increases with age, climbing
rapidly after age 50 and rare before age 40.
• Various criteria have been published to try and define “high risk” groups.
• Even the best collection of clinical findings such as the revised Bethesda
criteria will miss as many as 20% of the cases.
• Presently the search for inherited colon cancer is proceeding down two lines
of investigation, microsatellite instability and clinical findings.
• Microsatellites are DNA base pair repeats that are present
throughout the human genome.
• If they are altered or “unstable” then there is a chance that other
areas in the DNA could also be altered or mutated.
• In general, colon cancers that are unstable or Microsatellite
High(MSI high) are associated with Lynch Syndrome.
• Not all MSI-high colon cancers are hereditary. 15% of all colon
cancers are MSI-high and in this group between 3 and 5% are
associated with Lynch Syndrome.
• Lynch Syndrome is a group of disorders that share the same
mechanism and that is a faulty repair of misspellings of the DNA either one, or up to three base pairs at a time.
One of four enzymes are mutated in Lynch Syndrome MLH1, MSH2, MSH6, and PMS2
Patients with Lynch Syndrome are at increased risk for the
following cancers
• The classic hallmark for Lynch Syndrome has been, right
sided colon cancers, young age (under 50), multiple
generations of colon cancer or other lynch syndrome
associated cancers, multiple cancers in one individual,
and improved survival once diagnosed.
• Ohio State University screens ALL colorectal cancer
patients regardless of the above criteria and found the
incidence to be 7%.
• They found cases of Lynch syndrome in patients in their
70’s, left sided cancers, and little or no other family
members with colon or Lynch related cancers.
• This has lead to a national movement to screen
all colon cancers for Lynch.
• In Peoria your cancer can be checked for
Microsatellite stability and the presence or
absence of the Lynch associated enzymes.
• Based on these results you can be tested for a
specific mutation to see if you are carrying one
of these mutated genes.
• The other group of hereditary colon cancer syndromes
are associated with Microsatellite “stable” cancers.
• These include:
a) Familial Adenomatous Polyposis (FAP)
b) Attenuated Familial Adenomatous Polyposis
(AFAP)
c) Juvenile Polyposis
d) MUTYH associated polyposis (MAP)
e) Peutz-Jeghers syndrome
• Each disorder has a clinical picture and a specific genetic
marker.
• There are other syndromes associated with colon
cancer, such as Serrated Polyposis Syndrome - a
collection of a special type of polyps. There is no
marker for this disorder, but it carries an
increased risk of colorectal cancer.
• If you would like to discuss your family history
and colon cancer please make an appointment to
see us in our genetics clinic.