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Untitled Document
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| Colon
Cancer |
| Screening Procedures |
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By
Miriam Komaromy,
MD
Reviewed
by Peggy Conrad,
MS, CGC and Jonathan
Terdiman, MD
Last updated August 8, 2000
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There
are four commonly recommended procedures for both preventing
and detecting colon cancer: (For
recent news about upcoming techniques for detecting
colon cancer, see Related News below.)
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Fecal
Occult Blood Testing (FOBT)
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This
procedure, which is also referred to as stool guaiac testing
after the chemical that is used in the test, is employed
to detect microscopic amounts of blood in the stool, which
may indicate a bleeding polyp or cancer in the colon.
Since this test is usually performed on three successive
stool samples, your doctor will likely give you a kit
to collect the samples at home and then return them to
his or her office. The test can show blood in your stool
if you've ingested red meat prior to obtaining the samples,
so it's important that you follow your doctor's diet instructions
prior to taking the test. If one or more of the samples
tests positive for blood, you should undergo further testing
(colonoscopy) to find out where the blood is coming from
as well as to rule out the presence of a polyp or cancer.
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| Regular
(yearly) use of FOTB has been proven to reduce colon
cancer death by as much as 30 percent. |
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Regular (yearly) use of FOBT has been proven to reduce
colon cancer death by as much as 30 percent. It is also
the only test that has been shown to actually prevent
colon cancer from developing in the first place. However,
it's important to understand that not all polyps or other
types of malignant growths will bleed. Therefore, this
test may produce normal results even if you have colon
cancer. Because of this, doctors often will not rely on
this test alone to eliminate the possibility of cancer
in a particular patient, especially if there are other
symptoms or significant risk factors. Most commonly, FOBT
is performed every year and combined with flexible sigmoidoscopy
(see below) performed every five years. If both tests
are regularly used, the chance of colon cancer being detected
at a treatable stage is much greater than if either test
were relied upon alone.
For
news about the effectiveness of fecal occult blood testing,
see Related News below.
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Colonoscopy
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This
procedure, which is typically performed by a gastroenterologist,
is designed to examine the entire length of the colon
using a long, thin, flexible tube.
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| By
directly visualizing the inside of the colon, the
gastroenter-ologist can detect and remove polyps. |
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The tube has a light at the end and is connected to a
video monitor. By directly visualizing the inside of the
colon, the gastroenterologist can detect and remove polyps
(mushroom-shaped growths that may have the potential to
become cancerous) as well as other types of cancerous
growths or abnormalities.
If your physician recommends that you undergo a colonoscopy,
he or she will instruct you to first "prep"
your colon by cleaning it out the day before the procedure.
Usually the prep requires that you adhere to a liquid
diet the day before your procedure, and drink a special
cleansing solution the evening before the exam. The cleansing
solution allows you to pass all of the contents of your
colon before the exam (you'll spend a few hours in the
bathroom), so that the colon is completely empty at the
time of the exam.
You should be aware that different doctors may have different
"prep" instructions for you to follow, but their
goal is the same: to empty your colon (as much as possible)
before they begin the colonoscopy procedure.
When you arrive for your colonoscopy, you will be given
medication (a sedative and pain medication) to make you
comfortable during the examination. Your doctor will insert
in your anus a thin, flexible tube with a light and a
viewing camera at one end. He or she will then advance
the tube through your rectum and colon to the place where
your large bowel ends and your small bowel begins. At
that point, he or she will begin slowly pulling back the
tube in order to look for abnormalities on the inside
walls of the colon. Your doctor will also inflate your
bowel slightly (by pumping air into it) to make viewing
easier.
Patients are usually sedated but awake during the procedure, and typically experience little pain. The major risk of this procedure is perforation of the bowel wall, which is very rare (occurs in less than 1 of every 1,000 procedures). If your doctor finds a polyp during the procedure, he or she can remove it using the same tube that was employed to examine the colon. If any other type of abnormal growth is found in the colon, your physician can biopsy it to determine whether it is cancerous. (For recent news about risk of perforation, see Related News below.)
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| Regular
screen by colonoscopy probably has the capacity
to reduce the rate of colon cancer by 70 to 90 percent
in the general population. |
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Regular screening by colonoscopy probably has the capacity
to reduce the rate of colon cancer by 70 to 90 percent
in the general population. Indeed, many experts believe
that colonoscopy screening may prove to be the best strategy
to prevent colon cancer. However, many practical barriers
remain to routinely screening the entire adult population
— most prominently, the high cost and inconvenience
— with this test. Colonoscopy is therefore not
yet widely used as a routine screening test for colon
cancer but rather as a means of providing a more complete
evaluation of the colon if other tests that screen for
polyps (FOBT, sigmoidoscopy, barium enema) have come back
positive.
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Sigmoidoscopy
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Sigmoidoscopy,
which is also called flexible sigmoidoscopy to
distinguish it from the older and more painful rigid
sigmoidoscopy, is similar to colonoscopy. However,
it only explores the lower third to half of the colon.
Even though this procedure is a simpler undertaking than
colonoscopy, patients are more likely to experience pain
or discomfort — mostly commonly gaslike pains that
stem from the air used to inflate the bowel — since
they are rarely given an intravenous sedation for the
procedure. As is the case with colonoscopy, the procedure
carries with it the risk of bowel perforation, though
it is even less common with sigmoidoscopy than it is with
colonoscopy.
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| Sigmoidoscopy
is an easier procedure than colonoscopy, but only
detects polyps in the lower part of the colon. |
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A
sigmoidoscopy can be more quickly and easily performed
in a doctor's own office and is therefore less expensive
than full colonoscopy. For these reasons and more, a sigmoidoscopy
is more commonly used than colonoscopy to look for signs
of colon cancer. The drawback is that it cannot detect
polyps or cancers that are located deep within the colon
beyond the reach of the sigmoidoscope — an important
consideration for patients who have been diagnosed with
hereditary nonpolyposis colorectal cancer, or HNPCC, since
the polyps associated with this syndrome typically appear
higher up in the colon. (In other types of colon cancer,
polyps and cancers most often occur in the lower third
of the colon.)
Sigmoidoscopy reduces the rates of colon cancer by 60
to 80 percent for a patient who has polyps detectable
within the scope of its diagnostic reach. The problem,
of course, is that it will not reduce rates of colon cancer
for people who have polyps that have developed beyond
the reach of this scope. |
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Double-Contrast
Barium Enema
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This procedure, which is typically performed by a radiologist
and does not involve sedation, is designed to look for
polyps, cancers, and other abnormalities in your large
bowel (colon). If you undergo this procedure, the radiologist
will start by giving you a barium enema — white liquid
that's pumped into the colon through a thin tube inserted
into the rectum. (The barium coats the inside of the colon
so that it is visible on x-ray.) Next, the radiologist
will pump air into your rectum to separate the walls of
the colon and allow any polyps or masses to be seen on
x-ray. Finally, he or she is ready to perform the x-ray.
The major limitation of a double-contrast barium enema,
or DCBE, is that it doesn't allow your doctor to remove
or perform a biopsy on any detected polyps or masses directly.
Instead, it requires a follow-up colonoscopy. What's more,
it doesn't always do a good job of evaluating the lowest
part of your colon — the lower part of the recto-sigmoid
colon — which means that you may have to undergo
a sigmoidoscopy anyway once the DCBE has been completed.
Barium enema is good at detecting cancers and large polyps
but will miss a substantial proportion of small and medium-size
polyps. As a result, barium enema is rarely used these
days as an effective screening procedure for colon cancer. |
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References
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Selby,
J. et al. (1992). A case-control study of screening
sigmoidoscopy and mortality from colorectal cancer.
New England Journal of Medicine. 326(10): 700-2.
Mandel, J. et al. (1993). Reducing mortality from colorectal
cancer by screening for fecal occult blood. Minnesota
Colon Cancer Control Study. New England Journal of
Medicine. 328(19): 1365-71.
Mandel,
J. et al. (2000) The effect of fecal occult blood screening
on the incidence of colorectal cancer. New England
Journal of Medicine. 343(22):1603-1607.
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