CA-125

Overview
CA-125, also known as CA125, is an abbreviation for cancer antigen 125. CA-125 is a tumor marker or biomarker that may be elevated in the blood of some people with specific types of cancers. CA-125 is a mucinous glycoprotein and the product of the MUC16 gene.

Specificity and sensitivity
It is best known as a marker for ovarian cancer, but it may also be elevated in other malignant cancers, including those originating in the endometrium, fallopian tubes, lungs, breast and gastrointestinal tract.

CA125 may also be elevated in a number of relatively benign conditions, such as endometriosis, several diseases of the ovary, and pregnancy. It also tends to be elevated in the presence of any inflammatory condition in the abdominal area, both cancerous and benign.

Thus, CA-125 is not perfectly specific for cancer nor is it perfectly sensitive since not every patient with cancer will have elevated levels of CA-125 in the blood. For example, 79% of all ovarian cancers are positive for CA125, whereas the remainder do not express this antigen at all.

Use
CA-125 is clinically approved for following the response to treatment and predicting prognosis after treatment. It is especially useful for detecting the recurrence of ovarian cancer. Its potential role for the early detection of ovarian cancer is controversial and has not yet been adopted for widespread screening efforts in asymptomatic women. The key problems in using the CA-125 test as a screening tool are its lack of specificity and its inability to detect early stage cancers. An operation would be necessary to confirm that a woman with elevated CA-125 has ovarian cancer, with the associated risk of death from major surgery. In addition, even if cancer was confirmed in such circumstances, it usually would be at an advanced stage where therapy is less effective. The goal of many cancer biologists is to develop a test that would be employed to diagnose ovarian cancer at an early stage, when the effects of therapeutic interventions are optimal.

History
CA-125 was initially detected using the monoclonal antibody designated OC125. Dr.'s Robert Bast, Robert Knapp and their research team first isolated this monoclonal antibody in 1981.

Ranges in ovarian cancer
While this test is not generally regarded as useful for large scale screening by the medical community, a high value may be an indication that the woman should receive further diagnostic screening or treatment. Normal values range from 0 to 35 (u/mL). Elevated levels in post-menopausal women are usually an indication that further screening is necessary. In pre-menopausal women, the test is less reliable as values are often elevated due to a number of non-cancerous causes, and a value above 35 is not necessarily a cause for concern.

Related chapters

 * mucin

Resources

 * CA-125 blood test urban legend at snopes.com