The term tumor marker refers to any substance that can be detected in higher than normal amounts in the blood, urine or tissues of some patients with certain types of cancer. Tumor markers alone, however, are not sufficient to diagnose cancer for several reasons:
- Their levels can be raised in benign conditions;
- They are not elevated in every person with cancer (particularly in early-stage disease); and
- Many markers are not specific for a particular cancer (i.e., their levels can be raised in more than one type of cancer).
At present, most tumor markers are not used to diagnose cancer, but rather to monitor progression of the disease, evaluate the response to treatment, and check for tumor recurrence.
Purpose of Tumor Markers
- To help detect cancer
- To help determine the extent of malignant disease
- To monitor the effectiveness of anticancer therapy and detect recurrent disease before symptoms appear
- To detect cancer recurrence and determine the outlook (prognosis) for certain cancers
- The tumor marker prostate specific antigen (PSA) is now commonly used as a screening test to help diagnose prostate cancer.
Who Performs Tumor Markers
In this test, a doctor, a nurse, or a lab technician will draw the blood sample.
Special Concerns about Tumor Markers
- False-positive results are common with many tumor marker tests. For example, CA-125, a marker for ovarian cancer, is also elevated in nonmalignant disorders such as cirrhosis, pancreatitis, endometriosis, and pelvic inflammatory disease.
- False-negative results are also common. For instance, CA 19-9 is a marker for pancreatic or hepatobiliary cancer (affecting the liver and bile ducts), but its level is not elevated in about 30 percent of patients with pancreatic cancer or 35 percent of those with hepatobiliary cancer.
- Many tumor markers are not specific for a particular cancer. CEA, for example, is a marker for colorectal, pancreatic, gastric, lung, breast, and ovarian cancers.
- Borderline test results may pose a problem. For example, it is not clear whether all men with borderline PSA values—which may indicate prostate cancer or benign prostate conditions—should undergo a biopsy. In such cases, newer variations of the PSA test, such as the percent free PSA test, PSA velocity, and PSA density, may help clarify whether a biopsy is necessary.
- Certain medications may alter the results of the various tests.
- Pregnancy, normal menstruation, cigarette smoking, and various benign disorders may alter the levels of some tumor markers.
Before the Tumor Markers
Report to your doctor any medications, herbs, or supplements you are taking. You may be advised to discontinue certain of these agents before the test.
What You Experience during Tumor Markers
A sample of your blood is drawn from a vein, usually in your arm, and sent to a laboratory for analysis.
Risks and Complications of Tumor Markers
After the Tumor Markers
- Immediately after blood is drawn, pressure is applied (with cotton or gauze) to the puncture site.
- You are free to leave the testing facility.
- Resume taking any medications that were withheld before the test, according to your doctor’s instructions.
- Blood may collect and clot under the skin (hematoma) at the puncture site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
Results of Tumor Markers
- Your blood sample is sent to a laboratory for analysis. A variety of techniques may be used to isolate different tumor markers and quantify their levels. For example, a technique called serum protein electrophoresis—which uses an electrical field to differentiate blood proteins according to their size, shape, and electrical charge—is used to detect elevated immunoglobulin levels.
- A tumor marker assay is often used as an initial step in the diagnosis of cancer or cancer recurrence. Abnormal results necessitate additional tests, such as imaging studies and biopsy, to establish a diagnosis and determine the extent of the problem.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media