Colon Cancer Screening (cont.)
Who should consider genetic counseling and testing?
Genetic counseling followed by genetic testing should be considered for
individuals as well as their family members when there are:
- Individuals in the family with early onset of colon
cancer, before age 50
- Individuals in the family with numerous colon polyps
- Families in which multiple members have colon cancer
- Families with members with numerous colon polyps
- Families with members having colon cancers at young
ages
- Families with members having certain non-colon
cancers such as cancers of the uterus, thyroid, ureters, ovaries, small
intestine, etc.
Genetic testing without prior counseling is discouraged
because of the extensive family education that is involved and the complicated
nature of interpreting the test results.
Why is genetic counseling and testing important in hereditary colon cancer syndromes?
Patients who have hereditary colon cancer syndromes usually
have no symptoms and are unaware that they have colon polyps or early colon
cancers. They usually will develop colon cancers early in life (often before
ages 40-50). Therefore, to prevent colon cancers in patients with hereditary
colon cancer syndromes, colon screening must begin early. For example, patients
with FAP should have annual flexible sigmoidoscopies starting at age 12,
patients with AFAP should have annual colonoscopies starting at age 25, and
patients with HNPCC should have colonoscopies beginning at age 25 (or 10 years
younger than the earliest colon cancer diagnosed in the family, whichever is
earlier). The current screening recommendations for the general population
(fecal occult blood testing, flexible sigmoidoscopy, and colonoscopy beginning at ages 40-50) are
inadequate for most patients with hereditary colon cancer syndromes.
Genetic counseling and testing are important to identify
patients and family members with hereditary colon cancer syndromes so that
screening with flexible sigmoidoscopies and colonoscopies can begin early and,
if necessary, the colon can be removed surgically to prevent colon cancer.
Moreover, depending on which hereditary colon cancer syndrome is present, early
screening for other types of cancer such as ovarian, uterine, stomach, ureter, and thyroid may be
appropriate.
How is genetic testing conducted?
Genetic testing should be done following genetic counseling, so that family
members understand fully the advantages and limitations of genetic testing as
well as how the tests should be interpreted.
Within the family, the first person to undergo genetic
testing usually is the person who clearly has the disease (e.g., with numerous
colon polyps with or without colon cancer). If genetic testing of this family
member reveals a mutation responsible for a hereditary colon cancer syndrome,
then other family members can be tested for the same mutation. Those family
members who do not carry the mutation can be assured that they have not
inherited the syndrome, whereas those who have the mutation should begin early
screening for colon and other cancers. Depending on which syndrome is present
and the age of the patient, removal of the colon may be recommended.
Unfortunately, genetic testing that shows no known cancer syndrome does not
necessarily mean that there is no cancer syndrome. Our current knowledge about
colon cancer syndromes is imperfect and our ability to recognize them is
incomplete, and there may be unrecognized syndromes that cannot yet be detected.
Even if no cancer syndrome is identified by genetic testing, first-degree
relatives of someone with colon cancer are still considered at increased risk
for developing colon cancer themselves and should undergo early screening as
directed by their physicians.
Next: Summary of colon cancer screening »
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