How accurate is the Ca-125 blood test for ovarian cancer?

Larry E. Puls, MD
Gynecologic Oncology
Many cancers or unusual situations in the human body are associated with markers in the blood that can help physicians identify them. For example, when a woman is pregnant, a protein called HCG can be identified in her blood. The CA-125 is a tumor marker for ovarian cancer that can be detected with a blood test.
CA-125 is great test to help oncologists (cancer doctors) follow the course of the cancerous process in patients who have already been diagnosed with ovarian cancer. But CA-125 is not necessarily a great test for screening. Why? In women with early cancers of the ovary (meaning the cancer is only in the ovary), the test is positive just half of the time. In women with advanced disease (meaning the cancer has already spread), it is positive about 90 percent of the time.
We all wish this test were more useful for diagnosis because in patients who’s cancer is detected early, we have a high cure rate.
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