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== [http://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/tumor-markers-fact-sheet About Tumor Markers] ==

=== What are tumor markers? ===

Tumor markers are substances that are produced by cancer or by other cells of the body in response to cancer or certain benign (noncancerous) conditions. Most tumor markers are made by normal cells as well as by cancer cells; however, they are produced at much higher levels in cancerous conditions. These substances can be found in the blood, urine, stool, tumor tissue, or other tissues or bodily fluids of some patients with cancer. Most tumor markers are proteins. However, more recently, patterns of gene expression and changes to DNA have also begun to be used as tumor markers.

Many different tumor markers have been characterized and are in clinical use. Some are associated with only one type of cancer, whereas others are associated with two or more cancer types. No “universal” tumor marker that can detect any type of cancer has been found.

There are some limitations to the use of tumor markers. Sometimes, noncancerous conditions can cause the levels of certain tumor markers to increase. In addition, not everyone with a particular type of cancer will have a higher level of a tumor marker associated with that cancer. Moreover, tumor markers have not been identified for every type of cancer.

=== How are tumor markers used in cancer care? ===

Tumor markers are used to help detect, diagnose, and manage some types of cancer. Although 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.

Tumor marker levels may be measured before treatment to help doctors plan the appropriate therapy. In some types of cancer, the level of a tumor marker reflects the stage (extent) of the disease and/or the patient’s prognosis (likely outcome or course of disease). More information about cancer staging is available on the Staging page.

Tumor markers may also be measured periodically during cancer therapy. A decrease in the level of a tumor marker or a return to the marker’s normal level may indicate that the cancer is responding to treatment, whereas no change or an increase may indicate that the cancer is not responding.

Tumor markers may also be measured after treatment has ended to check for recurrence (the return of cancer).

=== Does NCI have guidelines for the use of tumor markers? ===
 
NCI does not have such guidelines. However, some national and international organizations do have guidelines for the use of tumor markers for some types of cancer:

*The American Society of Clinical Oncology (ASCO) has published clinical practice guidelinesExit Disclaimer on a variety of topics, including tumor markers for breast cancer, colorectal cancer, lung cancer, and others.
*The National Academy of Clinical Biochemistry publishes laboratory medicine practice guidelines, including Use of Tumor Markers in Clinical Practice: Quality RequirementsExit Disclaimer, which focuses on the appropriate use of tumor markers for specific cancers.

=== What tumor markers are currently being used, and for which cancer types? ===

A number of tumor markers are currently being used for a wide range of cancer types. Although most of these can be tested in laboratories that meet standards set by the Clinical Laboratory Improvement Amendments, some cannot be and may therefore be considered experimental. Tumor markers that are currently in common use are listed below.

== Common Tumor Markers ==