CA-125 Marker

For screening

CA-125 is a blood protein produced by the ovary that is used as a tumor marker since it is elevated in over 90 percent of patients with advanced ovarian cancer. Your doctor may order this test for screening if you have one or more risk factors for ovarian cancer. CA-125 is not used to screen the general population for ovarian cancer because there may be no increased level before the tumor causes symptoms. The test fails to find half of all early-stage cancers.

The presence of an elevated CA-125 marker does not necessarily mean you have ovarian cancer. Noncancerous conditions can also cause elevated CA-125 levels. For example, the CA-125 level may be elevated during the first trimester of pregnancy.

In treatment

The CA-125 test is used to evaluate the response to treatment, but is also used upon initial diagnosis and after treatment. Here are the three scenarios for using CA-125:

• Before chemotherapy. To establish a baseline high value. At this time the patient has experienced symptoms and the tumor is already at an advanced stage.
• During chemotherapy. To check that the CA-125 level is decreasing. This means that there is a response to therapy.
• After chemotherapy. To monitor for an increasing CA-125 level. This means that the cancer is starting to grow again.

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