Colorectal Cancer: Tests After Diagnosis
After a diagnosis of colorectal cancer, you'll likely need more tests. These tests
help your healthcare providers learn more about the cancer. They can help show if
it has grown into nearby tissues or spread to other parts of your body. The test results
help your healthcare providers decide the best ways to treat the cancer. If you have
any questions about these or other tests, talk with your healthcare team.
The tests you may have can include:
Lab tests of biopsy or surgery samples
Colorectal cancer is most often diagnosed by taking out and testing a small piece
of a polyp or tumor. This is called a biopsy. The tissue removed is called a sample.
When cancer was found, more tests may have been done on the sample. For instance,
certain lab tests are used to look for gene changes in the cancer cells. These tests
can help learn details about the cancer and show if certain types of treatment should
be used.
Blood tests
Complete blood count
A complete blood count (CBC) is done by taking a blood sample and checking it for:
Information from the CBC can help your healthcare provider know what the cancer is
doing to your body. For instance, a low red blood cell count (anemia) may be a sign
that the tumor is causing bleeding.
The CBC is also important during treatment and will be checked often. For instance,
it's important that your platelet count is high enough before you have surgery. Having
a low platelet count before surgery puts you at greater risk for bleeding. If you're
getting chemotherapy (chemo), your CBC needs to be watched. That's because chemo can
affect your bone marrow, which is where new blood cells are made.
Blood chemistry tests
Blood tests can be done to measure chemicals in your blood to see how certain organs,
like your liver and kidneys, are working. They may also show a possible spread of
the cancer to the liver.
CEA blood test
Your healthcare provider might do a test that measures a protein in your blood called
CEA (carcinoembryonic antigen). This protein is released into the blood by some colorectal
tumors. You might hear this called a tumor marker test. Tracking CEA levels can often
be a good way to see if treatment is working. The amount of CEA in your blood should
drop as more and more cancer cells are killed. After treatment, CEA levels can still
be tracked to see if they start to go up. This may be a sign that the cancer is coming
back.
Imaging tests
CT scan
Once a diagnosis of colorectal cancer is made, your healthcare provider needs to
make sure that the cancer is localized and hasn't spread. A CT scan can look for metastasis
in the liver, the most common location of colon cancer metastasis. A CT scan can find
colorectal cancer that has spread to your lymph nodes and lungs as well. The scan
takes X-rays of your body from many angles. You lie on a table that moves into the
center of the ring-shaped scanner, and a thin X-ray beam rotates around you. As the
pictures are taken, a computer makes detailed images of your insides. You might be
given an injection of a contrast dye through an IV (intravenous) line into your vein.
The dye helps any tumors show up clearly on the scans. A complete CT scan takes a
few minutes. You may have to wear a hospital gown during the test. You won’t feel
the scan. But some people feel uncomfortable having to lie still on a narrow table
during the test.
MRI
An MRI uses magnets, radio waves, and a computer to take pictures of the inside of
your body. An MRI doesn’t use radiation, and dye may not be needed. Your healthcare
provider may also ask for an MRI to better define lesions that showed up but were
unclear during a CT scan. It might be used to look for cancer in the liver, brain,
and spinal cord.
MRIs aren't painful. But they can take a long time to complete. They may take up to
an hour. During that time, you'll need to lie flat and still on a table that's moved
into a long narrow tube. If you don't like closed spaces, this test might be hard
to do. Talk with your provider about this. The equipment makes loud banging noises
during the scan. You can ask for earplugs if you think the noise will bother you.
PET scan
A PET scan can give the healthcare provider a better idea of whether an abnormal area
seen on a CT scan or other imaging test is cancer. This test can help see if the cancer
has spread to lymph nodes or other parts of the body. A PET scan can also be helpful
if your healthcare provider thinks the cancer may have spread, but doesn't know where.
A PET scan can give helpful information about your whole body. The picture isn't as
detailed as a CT scan. But it can be used along with a CT scan that was done at the
same time to look for tumors. This is called a PET-CT scan.
For this test, you are injected with a sugar that has a mildly radioactive substance.
Cancer cells absorb more of this sugar than normal cells, and the radioactive material
shows up during the image from the scan. To have the scan, you’ll need to lie still
on a table that slowly goes through the big rings of a PET scanner. This machine takes
pictures that show where the sugar is in your body. The whole process may take a few
hours. A PET scan is painless. But if you’re sensitive to the sugar, you may have
nausea, headache, or vomiting.
Ultrasound
Ultrasound uses sound waves to make pictures of the inside of your body. A small tool
called a transducer is moved over your skin. It gives off sound waves. The computer
picks up the echoes as they bounce off body organs. Ultrasound can be used to look
for tumors in your liver, gallbladder, pancreas, or other places in your belly. But
it can't look for tumors of the colon. For the exam, you lie on a table while the
transducer is moved along the skin over the part of your body being checked. Usually,
the skin is first greased or lubricated with gel. The test is painless and fairly
quick.
Two other kinds of ultrasound can be useful for colorectal cancer:
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Endorectal ultrasound. This can show how deep a tumor is in your rectum. It can also find lymph nodes that
might be cancer. This is important for finding out how advanced your cancer is. A
thin probe is put into your rectum through a tool called a proctoscope. The full exam
takes 5 to 10 minutes. It may be uncomfortable, but it isn’t painful. To get ready,
you'll need an enema the morning of the procedure.
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Intraoperative ultrasound. For this, the probe is put against your liver during surgery. This test can help
show if colorectal cancer has spread to your liver.
Chest X-ray
A chest X-ray can be used to see if the cancer has spread to your lungs. An X-ray
uses radiation to make a picture of the inside your body. The test is simple. It's
very good at showing lung nodules. It can also help show if you have lung or heart
disease.
Working with your healthcare provider
Your healthcare provider will talk with you about which tests you'll have. Make sure
to get ready for the tests as instructed. Ask questions and talk about any concerns
you have.