A new CA125-like antigen (CA602) recognized by two monoclonal antibodies against a newly established ovarian clear cell carcinoma cell line (RMG-II).

A cell line designated RMG-II was established from the ascites of a patient with ovarian clear cell carcinoma. The chromosomal analysis revealed aneuploidy with a hypertetraploid modal number and 8 marker chromosomes. Radioimmunoassay and immunocytochemical staining showed that RMG-II cells produced some tumor markers such as CA125 and TPA. Two monoclonal antibodies, designated MA602-1 and MA602-6, were generated by immunization of mice with an extract prepared from the culture supernatant of RMG-II cells. The epitopes recognized by these two monoclonal antibodies were proved to differ from the CA125 epitope, but to exist on the molecule bearing CA125. We developed a double-determinant sandwich enzyme immunoassay using these two monoclonal antibodies, and the antigen defined by this assay was termed CA602. CA602 was frequently found in the sera of ovarian cancer patients; the positive rates were 92%, 38%, 60%, and 80% for serous, mucinous, clear cell, and endometrioid ovarian carcinomas, respectively, when the cut-off value was set at 60 U/ml (= mean + 3SD of healthy females). CA602 levels in serum were also high in endometriosis patients and in early pregnancy, as is the case for CA125, and the correlation coefficient between CA602 and CA125 was high (r = 0.88). Our preliminary evidence suggests that this CA602 assay system has higher sensitivity than the CA125 one.