How accurate is the CA125 blood test for ovarian cancer?

David A. Fishman, MD
Gynecologic Oncology
The most commonly utilized test for ovarian cancer in clinical practice is the CA125 blood test. Overall, more than 80% of women with advanced stage epithelial ovarian cancer (EOC) have an elevated CA125 level. (The normal value is typically less than 35 U/mL.) However, levels are elevated in many different physiologic situations that are not always cancer. Moreover, the test is not useful for detecting asymptomatic early stage ovarian cancer because the results are only elevated in approximately 47% of women who have surgical confirmation that they have early stage disease (stage I).

Most gynecologic oncologists utilize CA125 for surveillance of EOC after the diagnosis has been surgically confirmed because it may be a sensitive indicator of persistent or recurrent disease. Unfortunately, CA125 is even less reliable for the detection of cancer in premenopausal women, since it is frequently elevated in noncancerous conditions such as pregnancy, endometriosis, uterine fibroids, liver disease, benign ovarian cysts, and in other malignancies such as colon, uterine, fallopian, gastric and pancreatic cancer.

CA125 screening for EOC in the general population is problematic; an elevated value accurately detects malignancy in less than 3% of women. Therefore, although it is the best available serum marker, CA125 does not have sufficient sensitivity to warrant its use as a sole marker to screen for ovarian cancer.

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