Tumor Marker Tests

Tumor markers are biochemical substances that are produced either by a tumor or by your body in response to the presence of cancer. If you have cancer, one or more of tumor markers may be present in higher than normal amounts, depending on the type of cancer you have. Tumor markers may be found in the blood, urine, or body tissues. Often, tumor marker levels are lower in early-stage disease (but still higher than normal) and higher with advanced disease. Their levels decrease in response to treatment and increase when the cancer progresses.

Tumor markers are often used to:

• Monitor response to treatment - Some tests show whether the cancer is responding to treatment.
• Monitor for progression - An increase in tumor markers may indicate disease progression.
• Detect recurrence - Regular monitoring of some tumor markers during a remission may help detect recurrence.
• Detect metastasis - Metastasis is the spread of cancer from its site of origin to another distant location in the body.
• Screen at-risk individuals - For example, prostate-specific antigen (PSA) is an example of a tumor marker that is very specific to one condition (prostate cancer). Because of this, it can function as a screening test for men who are at risk of prostate cancer, but have no symptoms.
• Identify a specific cancer subtype - Some cancers are divided into subtypes that are more or less aggressive; some tumor marker tests make it possible to distinguish between cancer types.
• Predict prognosis - Test results may indicate the chance of a negative or positive outcome based on outcomes of other patients with similar results.

Tumor markers are not specific enough to be used alone for diagnosing cancer. There are several reasons for this:

• Tumor marker levels can be elevated in people with benign (noncancerous) disease.
• Tumor markers are not elevated in every person with cancer, particularly those with early-stage disease.
• Most tumor markers are not totally specific for a single condition. A positive result may show that there is cancer, but not what type.

For these reasons, tumor markers are not used alone; instead, results from tumor marker tests are considered together with a patient's history, symptoms, and other test results.

New Advances in Tumor Marker Tests

Most tumor markers are proteins or other cellular products, such as hormones or receptors (molecules that permit the binding of other chemicals so that the cell can “receive” and respond to these chemicals). Tumor markers can also be the abnormal genes (particles containing DNA) in your body that cause a normal cell to become a cancer cell (oncogenes) or the products of such genes.

Genes determine which proteins will be produced by a cell and how they function. Oncogenes drive cells to produce proteins that cause the cells to behave as cancer cells, meaning they grow uncontrollably and spread. Researchers are developing methods to detect oncogenes. Even in many early-stage diseases, cancer cells may break away from the tissue where they originated and can be detected in the blood or other body substances.

This approach to tumor marker testing can be thought of as measuring the cause (gene) rather than the effect (protein). It may provide more accurate and useful information for screening, early detection, monitoring, and planning treatment.

Genetic testing for tumor markers as a way of enabling doctors to predict how patients are likely to respond to cancer treatments and deliver personalized treatment is rapidly advancing. A number of laboratory tests for women with breast cancer have been developed to predict how likely it is that the cancer will come back or whether chemotherapy will be effective. The tests analyze body fluids or tissues to determine which types of cellular genes are present and active. Knowing which genes are active helps doctors predict the behavior of cancer cells and their response to treatment. Examples of tests include:

MammaPrint^® is a test for women with breast cancer that detects the activity of 70 genes. This test is approved by the U.S. Food and Drug administration (FDA); many other genetic tests are not.

Oncotype DX^® is a test for women with breast cancer that detects the activity of 21 genes.

Because it is important for these tests to provide reliable, meaningful information to your doctor, the FDA is moving toward regulating the tests as medical devices.