Influence of human antimurine antibody on CA 125 levels in patients with ovarian cancer undergoing radioimmunotherapy or immunoscintigraphy with murine monoclonal antibody OC 125.

Human antimurine antibody responses interfere with CA 125 antigen determinations by crosslinking the murine antiovarian carcinoma monoclonal antibody OC 125 with the second murine radiolabeled antibody used in the CA 125 radioimmunoassay. Serial CA 125 levels in 22 patients with epithelial ovarian carcinoma undergoing either radioimmunotherapy or radioimmunoscintigraphy with iodine 131-labeled F(ab')2 fragments of OC 125 were followed up for up to 96 weeks after infusion. Fourteen radioimmunoscintigraphy patients received 131I-labeled monoclonal antibody by the intraperitoneal (n = 5) or intravenous (n = 9) route: 10 of 14 had sera drawn at appropriate time points for human antimurine antibody detection; 8 of 10 had 1.3- to 363-fold increases in CA 125; 4 of 8 had detectable human antimurine antibody (18.5 to 22 and 575 to 36 micrograms/ml). Eight radioimmunotherapy patients received 131I-labeled monoclonal antibody by the intraperitoneal route: 8 of 8 displayed an apparent 4.8- to 3725-fold increase in CA 125 levels within 7 to 42 days after monoclonal antibody infusion; 6 of 8 had detectable human antimurine antibody (13 to 4 and 319 to 31 micrograms/ml). Adsorption of immunoglobulin G resulted in a 21% to 98% reduction in CA 125 antigen levels in 4 of 4 patients tested. In patients with demonstrable human antimurine antibody, CA 125 antigen levels obtained by the clinical CA 125 radioimmunoassay are spuriously elevated.