Tumor markers are substances found at higher than normal levels in the blood, urine, or body tissues of some people with cancer. Although cancer cells often produce tumor markers, other cells in the body may also produce them. Tumor markers are also called serum markers or biomarkers.

Tumor markers and cancer

Along with other tests, tumor markers can indicate the presence of cancer. The most common uses of tumor markers include:

• Diagnosis—to confirm the results of other tests and symptoms (tumor markers alone are not used to diagnose cancer)
  
  
• Prognosis—to predict the cancer's behavior, response to treatment, and chance of recovery
  
  
• Monitor treatment—to determine how the cancer is responding to treatment
  
  
• Surveillance—to determine the likelihood the cancer will return after treatment
  
  
• Screening—to find cancer in healthy or high-risk people before symptoms develop

Limitations of tumor markers

Tumor markers are not foolproof. Usually doctors need results of other tests, such as x-rays or biopsies (removal of a tissue sample to check for cancer), to determine whether a higher level of a particular tumor marker is a cause for concern. Other limitations of tumor markers include the following:

• An elevated tumor marker level may indicate conditions or diseases other than cancer.
  
  
• Some tumor marker levels may be high in people without cancer.
  
  
• The level of the tumor marker may vary, making it hard to obtain consistent results.
  
  
• The measurement of a tumor marker may not rise until a person's cancer is advanced, which is not helpful for early detection or screening.

Testing for tumor markers

To test for a tumor marker, the doctor takes a sample of blood or urine and sends it to a laboratory. Tumor marker tests may also be taken from a biopsy sample. Some tests need to be repeated because the levels of tumor markers can change from month to month. This is called serial testing.

As with other laboratory tests, reliable tests for tumor markers need to be specific and sensitive.

• If the test is not specific, there is a chance that the results could indicate a tumor marker is present when it is not (a false positive). In this case, a healthy person may go through unnecessary tests and anxiety.
  
  
• If the test is not sensitive, the results may indicate a tumor marker is not present, when it actually is (a false negative). In this case, a person who may benefit from additional testing and treatment may not receive it.

Examples of tumor markers in cancer

These are examples of some common tumor markers associated with cancer. Please talk with your doctor or another member of your health care team to learn more about specific tumor markers.

Human epidermal growth factor receptor 2 (HER2) is a specialized protein on breast cancer cells that control cancer growth and spread. Women with tumors with high levels of HER2 benefit from certain drugs, including trastuzumab (Herceptin). Learn more about HER2 testing for breast cancer.

Carcinoembryonic antigen (CEA) may be found at elevated levels in people with different types of cancer, but it is most often associated with colorectal cancer. Read more about CEA and other tumor markers for gastrointestinal cancers.

Prostate specific antigen (PSA) is a protein made by the prostate gland. PSA levels are high in men with prostate cancer, prostatitis (inflammation of the prostate), or benign prostatic hyperplasia (BPH, a condition where prostate cells grow and block the flow of urine). A PSA test can be used to screen for prostate cancer; however, this issue remains under debate. Learn more about talking with your doctor about PSA testing. In addition, PSA tests are used to find out if prostate cancer has returned after treatment.

KRAS (pronounced kay-rass) is a gene that is changed, or mutated, in 30% to 40% of colon tumors. ASCO recommends that people with colon cancer that has spread outside the colon to other areas of the body should have a test to find out if the tumor has mutations in the KRAS gene. The test helps predict the patients that benefit from specific drugs. Find out more about KRAS testing for colon cancer.

Questions to ask the doctor

Consider asking the following questions of your doctor:

• What tumor marker tests do you recommend for me? Which ones have you already performed?
  
  
• How are these tests performed? How often should I have them?
  
  
• Can you explain the test results?
  
  
• If I have abnormal levels of a tumor marker, what does that mean? How does it affect my treatment?
  
  
• For cancer survivors: How is this tumor marker test used for my follow-up care?
  
  
• Where can I get more information?

More Information

What to Know: ASCO’s Guideline on Tumor Markers for Breast Cancer

What to Know: ASCO’s Guideline on Tumor Markers for Gastrointestinal Cancers

Additional resources

National Cancer Institute: Tumor Markers Fact Sheet

College of American Pathologists: MyBiopsy.org

Last Updated: February 02, 2010