http://www.covhealth.org/stellent/groups/public/documents/www/cov_014085.hcsp
Colon Cancer and CT Screening
What is colon cancer?
Cancers of the colon and rectum (colorectal cancer) are the second most common
cause of cancer deaths in the United States. It is estimated that there were
over 130,000 new cases and over 56,000 deaths in the United States in 2000.
This type of cancer happens in men more often than in women (54 versus 38 per
100,000 people per year). Most cases are diagnosed after 50 years of age. Most
patients with colon cancer (65%) present when the disease has already spread
elsewhere in the body and about one-half of these patients die within five
years. However, when found early, about nine out of 10 people survive.
Although colorectal cancer can occur in anyone, there are some people who have
a higher risk. Colorectal cancer is more likely to occur as people get older,
especially over 50. Colorectal cancer seems to be associated with diets that
are high in fat and calories and low in fiber. Polyps are benign growths on the
inner wall of the colon and rectum. Some types of polyps can change into cancer
and can be removed by placing a viewing tube into the rectum (sigmoidoscopy or
colonoscopy).
Research shows that women who have had cancer of the ovary, uterus, or breast
have a somewhat higher chance of also developing colorectal cancer. Parents,
siblings, and children of a person who has had colorectal cancer are also more
likely to develop colorectal cancer. If many family members have had colorectal
cancer, the chances increase even more. Ulcerative colitis is a disease in
which the lining of the colon becomes inflamed. Having this problem increases a
person’s chance of developing colorectal cancer. Another rare, inherited
disease called familial polyposis syndrome causes hundreds of polyps to form in
the colon and rectum. Unless this condition is treated, this disease almost
always leads to colorectal cancer.
Finding and removing polyps while they are still small helps to prevent
colorectal cancer. The CT screening test can find benign polyps that can
develop into cancers and screening can also find cancers. Researchers are also
looking at smoking cessation, using dietary supplements, using aspirin or
similar medicines, decreasing alcohol consumption, and increasing physical
activity to see if these can help decrease the incidence of colorectal cancer.
Facts about the colon CT screening scan of the abdomen and pelvis
Who should or shouldn’t have the scan?
The scan for colorectal cancer has been shown to be particularly useful for
individuals who have had colonoscopy performed, but where the examination did
not succeed in seeing the whole colon. Recent improvements in the CT scanning
equipment and techniques also show that this examination can be used to
complement the traditional examinations barium enema and colonoscopy for
evaluating people without symptoms of colon cancer. Currently, it is
recommended that people have their colon screened with colonoscopy or barium
enema every three to five years from the age of 50. This is particularly
important for people who have close relatives who have had colon cancer.
We believe that this test can be done instead of colonoscopy or barium enema in
certain people. However, if an abnormality is found, colonoscopy or other
procedures may be necessary. One advantage of this test over the others is that
it may be more comfortable for you than either the barium enema or the
colonoscopy. Cleaning out the colon is required for the CT scan (as it is for
the barium enema and colonoscopy) that requires a change in diet and using
laxatives and medications that cause frequent, liquid bowel movements before
the scan. At the time of the procedure, a small tube will be inserted into your
rectum and used to inflate your colon with air until you feel full. Scans will
be taken with you on your back and on your stomach. You must hold your breath
for several seconds at a time while scans are being taken. When the test is
done, you expel the air. The scan requires about 30 minutes to perform.
This CT screening test is also less risky than colonoscopy, from which a few
patients develop complications from the insertion of a larger tube into the
colon. Therefore, this test is particularly recommended for people who are
concerned about the risks or discomfort of the usual screening tests.
If you have already been diagnosed with colon cancer or have had a barium enema
or colonoscopy screening examination less than three years ago, you probably do
not need this test.
You may benefit most from a CT colon cancer screening test if:
You are over age 50 AND are an average risk individual AND have not had a colon
screening test for at least three years, or
You are 40 or over and are a high-risk individual AND have not had a colon
screening test for at least three years
How accurate is the scan?
The scan is very accurate at finding even small colon tumors, although a direct
colonoscopy may find more very small polyps. Using the scanners that we have
and the techniques that we use, we believe that it is as accurate as the usual
tests for important colon polyps larger than _ to 1 cm in size. However, this
test is relatively new and there is some disagreement about its accuracy. We
will be utilizing the newest techniques available to detect polyps of the colon
using CT technology. Much of the research evaluating this technology is still
ongoing.
Controversies about the scan
Is this scan proven to diagnose colon cancer?
As noted above, this is controversial. This test has been shown to find most
colon tumors and polyps, although it tends to miss very small polyps. However,
not many large studies have been completed yet and not everyone agrees that it
is proven to be as good a screening test as barium enema and colonoscopy.
Is this an experimental test?
Using CT to screen for colon cancer could still be considered experimental
because not enough research has been completed to prove without a doubt that it
is as accurate as the usual tests. However, a number of early studies do indeed
indicate that it is very accurate. There is a small risk from the radiation.
Other documentation detailing the risks from radiation can be made available to
you if you desire.
How the CT scan for colon cancer screening might help you.
As noted above, identifying a colon polyp or tumor by screening can increase
the chances of a complete cure to over 90% in many cases, compared to much
lower success rates for tumors once symptoms have occurred.
If I need a colonoscopy to further evaluate an abnormal CT exam will I need
another colon cleansing?
In most instances if you have an abnormal CT colon cancer screening test, you
will need another cleansing preparation of the colon prior to colonoscopy.
Arrangements can be requested to try and have a colonoscopy the same day or the
following morning after the CT screening colon exam. In that case you would not
need another colon cleansing. You would be notified when to return for the
colonoscopy either later that day or the next morning. The availability of
having a colonoscopy after the CT exam is not guaranteed.