Monoclonal antibody immunoradiometric assay for an antigenic determinant (CA 125) associated with human epithelial ovarian carcinomas.

CA 125 is an antigenic determinant expressed by greater than 80% of nonmucinous epithelial ovarian carcinomas. An immunoradiometric assay has been developed using a murine monoclonal antibody (OC125) to quantitate CA 125 in human serum. This immunoradiometric assay was optimized for specificity, sensitivity, and performance characteristics. Using a simultaneous immunoradiometric assay, the mean CA 125 concentration in 56 sera from healthy individuals was 11.2 +/- 5.4 (S.D.) units/ml, with 9.7 +/- 3.2 units/ml for 30 males and 13.1 +/- 6.8 units/ml for 26 females. A reference value of 35 units/ml included all 56 normals and excluded 86 of 105 (82%) ovarian carcinoma patients. This reference value also excluded 9 of 142 patients (6%) with benign diseases, but if the upper limit of normal was set at 65 units/ml, only 3 of 142 (2%) patients with benign diseases had elevated serum CA 125 levels, whereas 77 of 105 (73%) ovarian carcinoma patient sera remained positive. The ability of researchers, with this assay, to discriminate between CA 125 values in sera of patients with ovarian carcinoma and those of healthy individuals and patients with benign disease suggests that the assay deserves continued evaluation for monitoring and early diagnosis of ovarian cancer.