Screening tests are used to look for disease in people who do not have any symptoms. In many cases, these
tests can find colorectal cancers at an early stage and greatly improve the chances of successful treatment.
Screening tests can also help prevent some cancers by allowing doctors to find and remove polyps that might
become cancer. There are several tests used for colorectal cancer.
A newer kind of stool blood test is known as FIT (fecal immunochemical test). It is very much like the FOBT but
is perhaps a little easier to do and it gives a fewer number of false positive results. If it is positive, further tests
will be done.
Flexible Sigmoidoscopy (flex-sig): A sigmoidoscope is a slender, lighted tube about the thickness of a finger. It
is placed into the lower part of the colon through the rectum. This allows the doctor to look at the inside of the
rectum and part of the colon for cancer or polyps. Because the tube is only about 2 feet long, the doctor is only
able to see about half of the colon. The test can be uncomfortable but it should not be painful. Before the test,
you will need to take an enema to clean out the lower colon.
Virtual Colonoscopy: You might think of this as a super x-ray of the colon. Air is pumped into the colon to
cause it to expand, and then a special CT scan is done. Right now, this test is not among those recommended by
the American Cancer Society or other major medical organizations for finding colon cancer early. More studies
are needed to find out if it is as good as or better than other methods of finding colon cancer early.
Stool blood Test (fecal occult blood test – FOBT): This test is used to find small amounts of hidden (occult)
blood in the stool. A sample of stool is tested for traces of blood. People having this test will receive a kit with
instructions that explain how to take stool samples at home. The kit is then sent to a lab for testing. If the test is
positive, further tests, such as a colonoscopy, will be done to pinpoint the exact cause of the bleeding.
Colonoscopy: A colonoscope is a longer version of the sigmoidoscope. It allows the doctor to see the entire
colon. If a polyp is found, the doctor may remove it. If anything else looks abnormal, a biopsy might be done. To
do this, a small piece of tissue is taken out through the colonoscope. The tissue is sent to the lab to see if cancer
cells are present. This test can be uncomfortable. To avoid this, you will be given medicine through a vein to
make you feel relaxed and sleepy.
Barium Enema with air contrast: A chalky substance is used to partly fill and open up the colon. Air is then
pumped in to cause the colon to expand. This allows good x-ray films to be taken. You will need to use laxatives
the night before the exam and have an enema the morning of the exam.
How Is Colorectal Cancer Diagnosed?
Some of these tests are the same ones that are used for screening people who do not have symptoms.
Stool blood test, flex-sig, barium enema, and colonoscopy: your doctor may do one or more of these tests. They
were described earlier.
Blood tests: Your doctor will order a blood count to see if you have too few red blood cells (anemia). People
with colorectal cancer often become anemic because of bleeding from the tumor. You might also have blood tests
to check your liver function because colorectal cancer can spread to the liver causing problems. There are other
substances (tumor markers) in the blood that can help tell how well treatment is working. But these tumor markers
are not used to find cancer in people who have not had cancer and who appear to be healthy; rather, they
are most often used for follow-up of people who have already been treated for colorectal cancer.
Biopsy: In a biopsy, the doctor removes a small piece of tissue. The tissue is sent to the lab where it is looked at
under a microscope to see if cancer is present.
Ultrasound: Ultrasound uses sound waves to produce a picture of the inside of the body. Most people know
about ultrasound because it is often used to view a baby during pregnancy. This is an easy test to have. You simply
lie on a table while a kind of wand is moved over your skin.
Two special types of ultrasound might be used for people with colon or rectal cancer. In one, the instrument that
gives off sound waves is placed into the rectum. In the other test, used during surgery, the instrument is placed
against the surface of the liver to see if the cancer has spread there.
CT scan (computed tomography): A CT scan uses x-rays to take many pictures of the body that are then combined
by a computer to give a detailed picture. A CT scan can often show whether the cancer has spread to the
liver, lungs, or other organs. CT scans can also be used to help guide a biopsy needle into a tumor. CT scans take
longer than regular x-rays. The patient has to lie still on a table while the CT scan is being done. A contrast “dye”
may be injected or a special drink used to help outline the area being viewed.
A new way to use a CT scan is to do a “virtual colonoscopy.” After stool is cleaned from the colon and the colon is
filled with air, a computer can put together a picture of the inside of the colon. This method requires the same
preparation as for a colonoscopy and there is some discomfort from the bowel being filled with air. If anything not
normal is seen, a follow-up colonoscopy will be needed.
MRI (magnetic resonance imaging): Like CT scans, MRI displays a cross-section of the body. However, MRI uses
radio waves and strong magnets instead of radiation. As with CT scans, a contrast dye may be injected, although
this is used less often. MRI scans are helpful in looking at the brain and spinal cord. They take longer than CT
scans and you may have to be placed inside a tube. This can feel confining and upset people with a fear of closed
spaces.
Chest x-ray: This test may be done to see whether colorectal cancer has spread to the lungs.
PET scan (positron emission tomography): In this test, a type of radioactive sugar is used. The cancer cells
absorb high amounts of the sugar. PET is useful when your doctor thinks the cancer has spread, but doesn’t know
where. PET scans are now more accurate because they can be combined with a CT scan.
Angiography: For this test, a tube is placed into a blood vessel and moved until it reaches the area to be studied.
Then a dye is injected and a series of x-ray pictures is taken. When the pictures are complete, the tube is removed.
Surgeons sometimes use this method to find blood vessels next to cancer that has spread to the liver. The cancer
can then be removed without causing a lot of bleeding.
