Construction of an immunoradiometric assay for ovarian cancer associated antigen CA125 recognizing different antigenic determinant

We generated five murine monoclonal antibodies reactive with ovarian cancer-associated antigen CA125. These monoclonal antibodies seemed to bind to separate epitopes from OC125 antibody, known to recognize CA125. A series of immunoradiometric assays for measuring serum CA125 values rapidly and sensitively were devised using these monoclonal antibodies. The antigenic determinant of a new immunoradiometric assay was different from that of a currently used CA125 kit employing OC125 both as a catcher and a tracer. However, serum antigen levels were closely correlated to each other and were elevated not only in patients with ovarian cancer, but also in patients with endometriosis and in some normal females during menstruation. These results suggest that CA125 has at least two antigenic determinants close to each other and this new rapid assay is useful, although not specific for ovarian cancer, in patients with gynecological disorders.