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CA-125

What Does This Test Mean to You?

by Thomas J. Herzog, MD, and Robert L. Coleman, MD

Women who are suspected of having ovarian cancer and women who have been diagnosed with ovarian cancer often receive a blood test to measure their CA-125 level. CA-125 is a substance found in the blood called a glycoprotein (a sugar-associated protein). It is commonly referred to as a biomarker or tumor marker because it provides information about the biological state of a disease (ovarian cancer) and is obtained by a blood sample from which a level can be measured. But it is more accurately considered a tumor associated protein because elevated CA-125 levels do not always indicate ovarian cancer, and levels can be misleading.

The current CA-125 blood test is the second generation of the test that was first introduced in the early 1980s as a possible treatment. While researchers did not find a treatment, they did discover that blood levels of protein and antibody seemed to correlate with the status of the ovarian cancer. Closer investigation demonstrated that a CA-125 level of 35 units was found to be a useful cutoff point, with 99 percent of healthy women having values below this level.

The CA-125 test is most reliable and useful for the detection of recurrent disease in women previously diagnosed and treated for ovarian cancer.

How the CA-125 Test is Used in the Care of Women with Ovarian Cancer
The CA-125 test is used in a variety of situations during the course of the diagnosis, treatment, and follow-up care of ovarian and other closely related cancers, such as primary peritoneal and fallopian tube cancers. Four primary roles for CA-125 assessment have been established with varying degrees of clinical use and reliability:

To Inform Outcome
Several studies have linked the value of CA-125 to both short-term and long-term outcomes. The range of these investigations is a tribute to the value the test has in this disease and includes the likelihood initial surgery will be “optimal,” the likelihood all disease will be gone at first evaluation, the duration of survival or time until the tumor could recur, and the response to modalities of therapy, such as maintenance therapy. Unfortunately, these represent population trends and, individually, appear to be of less value.

To Detect Recurrent Disease
The CA-125 test is most reliable and useful for the detection of recurrent disease in women previously diagnosed and treated for ovarian cancer. While there are certainly exceptions to this statement, generally, rising numbers over a series of tests strongly suggest that a woman is experiencing a recurrence. This may be true even if the values are within the normal range, particularly if the CA-125 has been elevated in the past when disease was present. However, some women develop a recurrence without a rising CA-125 level. On the other hand, some women have a modest rise in the value but never develop recurrent disease.

To Monitor Treatment
The CA-125 test is a reliable tool to use along with a thorough history and physical exam to monitor treatment. However, its usefulness in this case depends on the starting value. Monitoring treatment results is most accurate when women have an elevated initial CA-125 value. It is vital to stress that this test represents just a piece of the puzzle and a number of other factors are considered in determining whether any given therapy is effective.

To Screen for Ovarian Cancer
As is the case with most cancers, early detection of ovarian cancers leads to a higher cure rate. There is not yet a highly effective screening test for ovarian cancer, and because the symptoms for this cancer are variable, many women currently are diagnosed at a later stage. Unfortunately, the CA-125 test, in isolation, has proven to be ineffective in screening for ovarian cancer. However, research is ongoing to look at other possibilities for ovarian cancer screening, including the use of a “cocktail” or panel of new markers in concert with CA-125.

We urge women diagnosed with ovarian cancer to try to keep in mind that the CA-125 test is only one indication of how well the treatment is working. Many other variables need to be considered, and the applications of CA-125 values need to be individualized. Talk to your doctor if you have questions about the CA-125 test.

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