Tumor Markers

Background

Tumor markers have generated a great deal of media interest. Used and interpreted properly, these tests may be the first clues to a hidden malignancy. These tumor markers are sometimes called onco-fetal proteins. As the name suggests, these proteins are present not only on tumors but also expressed in the fetal tissue during normal development. In normal individuals, these proteins are present at very low to undetectable levels. It should be noted though, that virtually any protein or chemical has the potential to be a tumor marker. For example, the serum calcium is greatly elevated in some cancers and may be a clue to the diagnosis. However, this elevation is not specific for any one type of cancer.

The following tests are commonly used for the monitoring and screening for cancers. After surgical removal of the tumor or obliteration by chemotherapy or radiation, the serum levels rapidly decline. Any recurrence of this tumor marker may indicate a recurrence of the tumor.

The following table illustrates some of the pitfalls in ordering tumor marker tests. It is adapted from the Dr. Henry's standard textbook of laboratory medicine, cited below.

RECOMMENDATIONS

Never rely on the result of a single test

When ordering serial testing, be certain to order every test from the same laboratory using the same assay kit

Be certain that the tumor marker selected for monitoring recurrence was elevated in the patient prior to surgery

Consider the half-life of the tumor marker when interpreting the test result

Consider how the tumor marker is removed or metabolized from the blood circulation

Consider ordering multiple markers to improve both the sensitivity and the specificity for diagnosis

Order the nonspecific markers for cost-saving and for their high sensitivity

Be aware of the possibility of a hook effect

Be aware of the presence of ectopic tumor markers

Clinical Diagnosis and Management by Laboratory Methods. 20th Edition. Henry JB. WB Saunders 2001.

Commonly Used Terms

Alpha-fetoprotein

CEA

CA15-3

CA19-9

CA 125

Her 2

HCG (Human chorionic gonadtropin)

PSA (Prostate specific antigen)

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Last Updated 1/14/2003