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What is it?

CA125 (cancer antigen 125) is a protein or so-called tumour marker that may be elevated in the blood of some patients with specific types of cancer. The CA125 level is determined by a blood sample and is usually present in greater concentrations in ovarian and other gynecological cancers and in some abdominal cancers.

CA125 blood test is used in conjunction with other tests – CT/PET scan, transvaginal ultrasound and a rectovaginal examination to diagnose ovarian cancer. The CA125 is also used to monitor women with known ovarian/ gynecological cancer; it is used in evaluating your treatment progress and outcome as well as recurrence.

Because of its importance in monitoring chemotherapy treatment, patients are often fearful or fixated on the absolute number. A normal value is less than 35 U/ml. A doubling of this number can be indicative of disease progress.  However, CA125 levels can be high in a number of benign conditions including endometriosis, pelvic inflammatory disease, fibroids, pancreatic conditions, auto-immune disease and heart and lung disease to name a few. There is no real "normal" for any patient nor are higher values necessarily indicative of disease volume.  Patients have been diagnosed with advanced ovarian cancer in absence of an elevated CA125 and others have enjoyed years of remission with numbers in excess of the “normal”.

Conventional Wisdom:

Health practitioners often discourage patients from following the results of a CA125 test too regularly and too closely in absence of symptoms. It has been shown that patients can actually increase the value by stress and worry. It is important to remember that the test is a guideline and not a diagnosis.

Self Help:

Because the CA125 test is taken as a routine part of your checkup, it is important to keep its purpose in perspective and remember that it is not always a good indicator for every patient. As mentioned above, patients can develop a "CA125 psychosis" whereby their stress and worry actually affect the outcome. A number greater than 35 U/ml can alert you to be more mindful of what's going on in your body and heighten a sense of awareness to changes. Conversely, a value less than 35 U/ml can be the source of great encouragement during chemo treatment.

Ultimately, most clinicians rely on the adage “Treat the patient, not the number”.


Additional Information:

The following paper from TheOncologist provides more information on the usefulness and limitations of CA125:

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