INTERFERENCE BY HUMAN-ANTIBODIES WITH TUMOR-MARKER ASSAYS

Many cancer patients respond to the in vivo application of murine monoclonal antibodies with the formation of various human antibodies which can interfere with tumor marker assays, While interferences by nonspecific human anti-mouse antibodies can be eliminated by addition of nonspecific mouse IgG, special problems can occur when the antibody applied in vivo also is employed in the in vitro assay, In ovarian cancer patients treated with the anti-CA-125 antibody OC125 and with the anti-TAG-72 antibody B72.3, respectively, we measured erroneous values for the tumor associated antigens CA-125 and TAG-72 due to human antiidiotypic or antiantudiotypic antibodies, These interferences can only be prevented by using reagent antibodies different from the antibody applied in vivo. However, because it is difficult to eliminate interferences completely, tumor marker values determined in patients treated with monoclonal antibodies should be interpreted with care.