Tumor Markers: A Guide to Laboratory Testing
Tumor markers are substances that can sometimes be measured in blood, urine, or tissue and may be elevated in certain cancers. They are useful tools in specific situations, but they are not screening tests for cancer in the general population and cannot diagnose cancer on their own. This guide explains what tumor markers are, how they are used, and what their results do and do not mean.
Key takeaways
- Tumor markers are substances produced by cancer cells or by the body in response to cancer, and they can be measured in blood, urine, or tissue.
- A single tumor marker test generally cannot confirm or rule out cancer; results must be interpreted with imaging, biopsy, and clinical findings.
- Some tumor markers are used to monitor response to treatment or detect recurrence in people already diagnosed with cancer.
- Not all cancers produce measurable tumor markers, and benign conditions can also raise marker levels.
- Tumor marker tests are not recommended as general screening tools for cancer in people without symptoms or a known diagnosis.
What Are Tumor Markers?
Tumor markers are biological substances that can be detected in higher-than-normal amounts in the blood, urine, or body tissues of some people with cancer. They may be produced directly by cancer cells or by normal cells in response to a cancer's presence. Common examples include prostate-specific antigen (PSA), carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), CA-125, CA 19-9, and CA 15-3. Each marker is associated with certain cancer types, but none is exclusive to a single disease.
Because tumor markers can also rise with benign conditions such as inflammation, infection, or liver disease, an elevated result does not automatically mean cancer. Likewise, a normal result does not rule cancer out. This is why tumor marker tests are generally used as one piece of a larger clinical picture rather than as stand-alone diagnostic tools.
How Tumor Marker Tests Are Used
Tumor markers are most often used in three settings: monitoring how well a known cancer is responding to treatment, checking for recurrence after treatment has ended, and sometimes helping to guide treatment decisions. For example, PSA is used to monitor prostate cancer, CA-125 may be followed in ovarian cancer, and AFP is used in certain liver and germ cell tumors. In these contexts, trends over time are usually more informative than a single measurement.
Tumor markers are occasionally used alongside other tests to help evaluate a suspicious finding, but they are not typically used to screen for cancer in people without symptoms. Screening recommendations from major health organizations generally rely on imaging, physical examination, or other validated methods rather than tumor marker blood tests, because marker tests alone have not been shown to reduce deaths from most cancers when used for screening.
Limitations and False Results
One of the main limitations of tumor markers is that they lack both sensitivity and specificity. Sensitivity refers to how often a test is positive in people who actually have the cancer; specificity refers to how often it is negative in people who do not. Many markers are elevated in only a fraction of people with a given cancer, and many can be elevated in people without cancer at all. This overlap makes it difficult to use a single marker to make a diagnosis.
False positives can lead to unnecessary worry and additional testing, while false negatives can provide false reassurance. Because of these limitations, results are interpreted by a physician in the context of the person's history, symptoms, physical exam, imaging studies, and biopsy results. A biopsy, in which a tissue sample is examined under a microscope, remains the standard for diagnosing most cancers.
Interpreting Your Results
If you have a tumor marker test, the result will be reported with a reference range that varies by laboratory and by the specific marker. Values slightly above or below the reference range may not be meaningful on their own. Your physician will consider the result alongside other information, including whether you have a known cancer diagnosis, what treatment you have received, and what previous marker levels looked like.
It is important to ask your physician what a specific result means for your situation and whether repeat testing or additional evaluation is needed. Trends across multiple tests over time often matter more than any single value. If you are being monitored for a known cancer, your care team will typically explain how marker results fit into your overall treatment plan.
Frequently Asked Questions
Can a tumor marker test diagnose cancer?
No. Tumor marker tests alone cannot diagnose cancer. Diagnosis generally requires a biopsy and examination of tissue by a pathologist, along with imaging and clinical evaluation.
Are tumor markers used for cancer screening?
In general, no. Major health organizations do not recommend tumor marker blood tests as routine screening for most cancers in people without symptoms, because the tests have not been shown to reliably reduce deaths when used this way.
What does it mean if my tumor marker level is elevated?
An elevated level may be caused by cancer, but it can also result from benign conditions such as inflammation, infection, or liver disease. Your physician will interpret the result along with your history, symptoms, and other tests.
Why do tumor marker levels change over time?
Levels can rise or fall with treatment, disease progression, or unrelated conditions. Because of this, doctors often look at trends across several tests rather than a single measurement.
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