CA 125

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Medical Author:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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What is CA 125?

CA 125 is a protein that is a so-called tumor marker or biomarker, which is a substance that is found in greater concentration in tumor cells than in other cells of the body. In particular, CA 125 is present in greater concentration in ovarian cancer cells than in other cells. It was first identified in the early 1980s, and the function of the CA 125 protein is not currently understood. CA stands for cancer antigen.

How is CA 125 measured?

CA 125 is usually measured from a blood sample. It can also be measured in fluid from the chest or abdominal cavity. The tests currently in use are all based upon the use of an antibody that is directed against the CA 125 protein (monoclonal antibody technique).

In 1996, an improved version of the test was introduced and is sometimes denoted as CA 125 - II. The numerical figure of the second generation test results may be higher or lower than a first generation test. When comparing multiple test results over time, it can be important to know which method was used.

What is the normal range for CA 125?

The normal values for CA 125 may vary slightly among individual laboratories. In most laboratories, the normal value is less than 35 U /ml.

What does an elevated CA 125 mean, and how is the test used?

It is not possible to interpret the meaning of an abnormally high CA 125 without additional information about the particular patient being evaluated. The reason is that blood levels of this protein can be increased in many different benign and malignant conditions. The two most frequent situations in which CA 125 is used is to monitor patients with a known cancer (malignancy) or as one of several tests in the workup of a patient suspected of having a tumor.

The most common use of the test is the monitoring of women with known cancer of the ovary (ovarian cancer). In the patient who is known to have a malignancy, such as ovarian cancer, the CA 125 level can be monitored periodically. A decreasing level generally indicates that therapy, including chemotherapy, has been effective, while an increasing level indicates tumor recurrence. Because of test variation, small changes are usually not considered significant. A doubling or halving of the previous value would be important.

In the patient who is being evaluated for a pelvic mass, a CA 125 level greater than 65 is associated with malignancy in approximately 90% of cases. However, without a demonstrable mass, the association is much weaker.