MONITORING CANCER ANTIGEN-125 IN SERUM OF OVARIAN-CANCER PATIENTS AFTER ADMINISTRATION OF I-131-LABELED F(AB')2 FRAGMENTS OF OC125 ANTIBODY

We evaluated the effect of repeated administration of OC125 F(ab')2 fr agments on cancer antigen (CA) 125 determination in 21 0 serum samples from 30 patients. We found falsely high CA 125 concentrations in 142 (68%) samples, using a homologous CA 125 enzyme immunoassay (EIA) with OC1 25 antibodies. The Truquant OV2 method, which involves two other murine antibodies, and the IMx CA 125 method, which uses sheep antibod ies as capture antibodies, resulted in only slightly increased (false- positive) values in some samples with exceptionally high CA 125 EIA va lues. We measured falsely low CA 125 values in 37 (18%) samples with t he Truquant OV2 method. Interferences could be eliminated by removal o f serum IgG. Our results suggest that interferences are to some extent caused by anti-idiotypic IgG induced by OC125 administration. Assays involving nonmurine anti-CA 125 antibodies as capture antibodies seem to be most suited for CA 125 determination after OC125 treatment, but in every case an apparent increase of CA 125 after OC125 infusion shou ld be validated.