Different antigenic nature in apparently healthy women with high serum CA 125 levels compared with typical patients with ovarian cancer.

BACKGROUND. CA 125 is a representative ovarian cancer-associated antigen defined by monoclonal antibody OC125. Recently, monoclonal antibodies were produced (designated 130-22 and 145-9) that were reactive with CA 125 but bound to a separate epitope named CA 130. There was a close correlation between serum CA 125 and CA 130 values in most instances. However, among more than 8000 serum samples, 5 apparently normal women had high serum CA 125 values, despite having normal CA 130 values. In this study, the antigenic nature of these five women was investigated. METHODS. Using gel chromatography, the molecular masses of CA 125 and CA 130 were estimated that were found in the five women with false-positive CA 125 values. The sera were examined using double-determinant assays combining iodine-125-labeled OC125 or iodine-125-labeled 130-22 with OCI25-coated or 145-9-coated beads. RESULTS. The molecular masses of both CA 125 and CA 130 were estimated as greater than 1000 kilodaltons (KD); the CA 130 mass from one of the five women with an abnormal CA 125 level was approximately 200 KD using gel chromatography. Using the double-determinant assays that combined iodine-125-labeled OC125 or iodine-125-labeled 130-22 with OC125-coated or 145-9-coated beads, high radioactivity was found only in the homologous assay using iodine-125-labeled OC125 with OC125-coated beads. These results suggest that the antigenic nature of CA 125 found in apparently healthy women differs from that found in patients with ovarian cancer and that CA 130 epitopes are not present. CONCLUSIONS. Measurement of serum CA 130 concentrations may be useful for excluding women with falsely elevated CA 125 values.