Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
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.
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.
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