Tumor Markers and Diagnosing Colon Cancer

Colon cancer
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After successfully beating colon cancer, one of the most important things you can do to care for yourself is to continue with your follow up appointments and testing. Catching recurrent cancer early is just as important as your initial early diagnosis of colorectal cancer. There are many different ways your oncologist and gastroenterologist can continue to follow and monitor your cancer, but one of the simplest is via the tumor markers in your blood.

If you have, or have had cancer, these substances can present in higher amounts in your blood stream, and might help your doctor guide your need for additional testing and closer monitoring.

There is not one general tumor marker for all cancers -- science has found specific tumor markers --which might be in your blood, urine, or even the tumor itself, that pair to specific cancers. There are commonly identified tumor markers specific to colorectal cancer to include the carcinoembryonic antigen (CEA), KRAS gene mutation, and the cancer antigen 19-9 (CA 19-9). CEA and CA 19-9 are found in the blood stream, whereas the KRAS mutation is found in the actual tumor. Blood levels of CEA and CA 19-9 can be elevated for reasons other than cancer, such as for inflammation in the body, and are not a reliable diagnostic tool for screening purposes. 

Likewise, the tumor markers present in your blood are specific to you – one CEA test won’t prove anything.

You may naturally produce a higher amount in your blood stream than someone else of your age and gender.

Your Doctor Cannot Diagnose Colon Cancer with a Blood Test

For that matter, your doctor cannot diagnose a recurrence with a simple blood test either. What he or she can do is monitor your tumor markers over time and watch for trends, as well as using the levels to gauge your response to treatment options.

Checking the levels every three to six months following surgery for bowel cancer is the current recommendation, for a period of up to six years.

To have a definitive diagnosis of recurrence, you will have to undergo another biopsy. Your doctor needs to see your pathology report prior to diagnosing you and discussing treatment options. He or she may also request more tests, such as a PET or CT scan, to determine if there is any metastasis, or spread of your colon cancer to other organs, prior to suggesting your treatment.

How Do I Get Tested?

To test your CEA levels, a simple blood sample will be taken and your doctor will send it off to a lab for testing. When you talk to your doctor about your results keep this in mind: Blood tests are not infallible. There is a chance of false positive and false negative results. A false positive CEA would mean that the test shows that the tumors are returned or growing, when in fact they are not. A false positive test can increase your stress and worry – potentially for no reason at all. Likewise, there is also the chance for a false negative test, meaning that the test reflects the absence of markers when in fact, there is a growing tumor present.

KRAS gene mutations are not present in everyone with colon cancer. However, if you do have the mutation, your doctor can use this knowledge to decide which medications might best help you fight the cancer.

Keep Your Appointments

Even though a simple blood test monitor for recurrence might sound appealing, it is highly encouraged that you do not skip out on your other recommended follow up tests such as the colonoscopy. CEA and other tumor markers should be used as a tool alongside your routine follow up appointments, not to replace them.


Cancer.Net. (n.d.). Follow Up Care for Colorectal Cancer. Accessed online June 22, 2015.

National Cancer Institute. (n.d.). Tumor Markers. Accessed online June 29, 2015.

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