How Accurate Are Tumor Markers?


There are many questions associated with breast cancer testing and their accuracy. Do tumor markers give accurate understanding of what's happening in an person's body? Why do some doctors use the test and some do not? These are just a couple of the questions we need answered.

Breast cancer can be confusing, especially to those of us who are armchair oncologists. It’s pretty normal to play the compare and contrast game with our diagnoses, or at least that’s what I’ve found in the breast cancer community. When I heard some of my friends talking about their biomarker tests, I felt left out. I had no idea what they were talking about. They were comparing their numbers in a matter-of-fact way, not in a one-up-manship kind of way. Timidly, I asked for an explanation and was quickly given a response. They wondered why my oncologist hadn’t performed a biomarker test and I couldn’t help but wonder, too. Surely he’d tested me, but just to make sure, I went through copies of my medical reports. I didn’t even have a clue what I was looking for so I had to ask. My breast cancer friends instructed me to look for tests named CA 125 or CA 15-3/CA 27.29. With that information, I thumbed through my records again. There were no such tests. Wanting to understand what these tests were and why they hadn’t been performed on me, I consulted Dr. Google.

Information I found included the following: Tumor markers are also known as biomarkers. They are substances found in the blood at elevated levels when advanced cancer is present in the body. There are about 20 different kinds of tumor markers but only three are specific to breast cancer. Those are identified as CA15-3, CA27.29, CA-125, and Carcinoembryonic antigen (CEA). Most tumor markers are made by normal cells as well as by cancer cells, but they are produced at higher levels in cancerous conditions. These substances can be found in blood, urine, tissues, and other bodily fluids of some patients with cancer. Most tumor markers are proteins but there have also been gene expressions and changes to DNA that can also be used as tumor markers. A universal tumor marker, with the ability to detect any type of cancer, has not been found.

According to the website,, “Tumor markers are used to help diagnose, detect, and manage some types of cancer. An elevated level of a tumor marker may suggest the presence of cancer, this alone is not enough to diagnose cancer. Therefore, measurements of tumor markers are usually combined with other tests, such as biopsies, to diagnose cancer.” According to another website,, “Tumor marker tests may also be used to screen for cancer in people with high risk of the disease. Some may be done to learn more about the cancer when it is first diagnosed. However, the presence or amount of a tumor marker alone is not enough to diagnose cancer.”

There has been no evidence to prove that tumor markers are 100 percent reliable for determining the presence or absence of cancer. Many circumstances, such as other health issues or disease, can contribute to raised tumor marker levels. There have also been incidences of increased tumor marker levels in people with no active cancer. Blood samples for tumor markers can vary over time and may make obtaining consistent results difficult. In the beginning stages of cancer, there may not be enough cancer cells present to give a clear picture of what’s going on in the body so early testing could be inaccurate.

Blood or urine tests are used to measure tumor marker levels in the body. These samples are sent to a laboratory for specific evaluation. The results from these tests can result in a false positive or a false negative report. Without complete accuracy, false positive or false negative results can be distressing to the patient and could suggest a tumor is present or growing despite aggressive treatment.

After reading the pros and cons of tumor marker tests, I felt more at ease, but at my next appointment, I confronted my oncologist. I asked why I had not been tested. I explained I’d feel better knowing my tumor marker level. He looked at me and explained he didn’t feel the need to test me. Still, I wanted to know. I felt I would have a better idea where I stood if I had a concrete number to grasp.

Last week, I left my original oncologist and moved under the care of a local cancer treatment facility. One of the first tests performed at the new location was a blood test. When I asked what they were looking for, I was surprised to find they were performing tumor marker tests. I received copies of the test reports via email. As I scrutinized the results, I found I’d been tested for the CA 15-3 and CA 27.29 markers. My CA 15-3 marker was 26.8. My CA 27.29 marker was 28. Now I had concrete numbers but had no idea what normal levels were so I didn’t feel secure. Once again, I consulted Dr. Google for normal ranges on these tests. I found that readings under 30 were considered to be within the normal range. I felt better knowing I had numbers that fell under the normal range, but was my security a false security? Did the biomarker or tumor marker tests really give an accurate view of my cancer situation? Was I really cancer free? What if the tests weren’t accurate and cancer was actively growing inside my body? I needed more information so I shared my concerns with my new oncologist. She informed me the tests were just a reference. Some oncologists use the tests and some do not. She felt they were helpful and would continue to periodically test my levels. She assured me she would never replace more diagnostic tests such as PET scans, MRIs, and bone scans with tumor marker levels. I have a bone scan scheduled for August 10th and I’m sure those results, along with the tumor marker levels, will give my doctor a more accurate view of what’s going on in my body.

If you haven’t had a tumor marker test performed, don’t feel slighted. The test levels may be a good indicator of your situation and then again, they may not. As with all medical tests and procedures, there are many variables to consider and we need to leave that up to the trained professionals instead of the arm chair wannabes.


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