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.