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CA125 is a protein in the blood that is sometimes elevated in women with ovarian cancer. The CA125 blood test is used to follow up women who have already been diagnosed with ovarian cancer, in order to monitor response to treatment and to look for recurrence of the cancer. Some researchers have looked at CA125 to detect ovarian cancer in women with ovarian abnormalities or in women who are at high risk for ovarian cancer. The test is considered neither sensitive nor specific for finding ovarian cancers in high-risk women. However, some studies found the test, particularly in combination with transvaginal ultrasound, might detect some ovarian cancers before symptoms appear. In a recent small study which looked at surveillance in high-risk women, CA125 and transvaginal ultrasound identified six cases of advanced ovarian cancer. The authors concluded that ovarian cancer surveillance was ineffective in this population. Research from a large study on ovarian screening known as GOG 199 found that premenopausal women have higher normal CA125 than postmenopausal women. Based on this, the reference ranges for normal CA125 in premenopausal women may change, making the test less likely to produce false positives.
Another study which reviewed published research on ovarian cancer detected through screening concluded that high grade serous ovarian cancer (the type of cancer that usually develops in mutation carriers) is more likely to be diagnosed at advanced rather than early stage, even if found during screening.