Serum CA-125 in the evaluation of benign adnexal cysts.

Because serum CA-125 concentrations are increased in women with endometriosis, our objective was to determine whether CA-125 levels could be used to differentiate endometriotic from nonendometriotic benign cysts. During a 2-year period, all women who had an endometrioma (n = 33) or a nonendometriotic cyst (n = 27) that was greater than or equal to 4 cm were included. Serum CA-125 levels were measured by an immunoradiometric assay, and the mean concentrations in women with an endometriotic cyst increased as the diameter of the cyst increased. The mean CA-125 concentrations in women with cysts greater than or equal to 4 cm were 53 +/- 2 U/ml in 19 women with an endometriotic cyst, 11 +/- 1 U/ml in 20 women with a nonendometriotic cyst, and 15 +/- 1 U/ml in 7 women with a nonendometriotic cyst and endometriosis. In the fluid of 10 endometriomas, the mean CA-125 concentration was 290 +/- 94 X 10(3) U/ml (range 10 to 900 X 10(3) U/ml). With cysts diameters greater than or equal to 4 cm, 19 of 19 women with endometriotic cysts, zero of seven women with nonendometriotic cysts and endometriosis, and zero of 20 women with nonendometriotic cysts had CA-125 concentrations greater than or equal to 20 U/ml (99% upper normal limit). We conclude that serum CA-125 determinations offer an excellent method to differentiate endometriotic from nonendometriotic benign cysts.