[False positive of DUPAN-2 caused by IgM-human anti mouse antibody].

We investigated a case in our experience presenting false-positive for DUPAN-2 by IgM-human anti mouse antibody (HAMA). A female aged 40s has been treated in our hospital from 2003. Her serum level of DUPAN-2 in 2005 and 2006 were 110 U/mL and 140 U/mL respectively. While this level was increased to 770 U/ml in 2007, and kept in the higher level so far. Around years of 2007, no meaning changes was detected by radiological and laboratory tests, and there was no significant change in her clinical signs and symptoms and medications. The elevation of DUPAN-2 was thought as a false-positive phenomenon and the mechanism was investigated. As results, no dilution lineality was found, and absorption test showed a 95% reduction of DUPAN-2 levels not by IgG and IgA, but IgM-specific antiserum. Dithiothreitoldeacylation test with neuraminidase, and absorption test with HBR-1, IIR, and mouse IgM serum, it was suggested that the IgM with HAMA activity of the patient reacted with mouse monoclonal antibodies in reagents. Moreover, the HPLC-eluted fraction of DUPAN-2 of this patients was detected in the fraction of IgM, which as different from that of a control pancreatic cancer patient. Above these data, elevation of DUPAN-2 in this patient was a false positive phenomenon by IgM-HAMA reacting with mouse monoclonal antibodies in reagents. Although there are few reported cases of false positive phenomenon in DUPAN-2 measurement, we have to pay attention to such phenomenon when detecting an unlikely higher levels that could not be explained by clinical information.

[Examination of the patient serum presenting a CEA false high value after cancer immuno-cell therapy].

False positive elevation of carcinoembryonic antigen (CEA) was observed in a 65-year-old woman who was treated with dendritic cell therapy (DCT) and activated lymphocyte therapy (ALT) for intrahepatic cholangiocarcinoma. Three months after the initiation of these therapies, her CEA value measured by AIA (TOSOH) began to increase without any evidence of worsening of cholangiocarcinoma. CEA was measured by several different methods, and only the result measured by AIA was high, indicating the presence of a false positive phenomenon. To clarify this phenomenon, we evaluated the patient's serum precisely. Gel filtration chromatography of her serum showed that CEA was detected in the elution fraction of IgG, which was different from the reference samples. Furthermore, this peak disappeared after incubation of patient's CEA and HBR-1. The immunoglobulin absorption test revealed that CEA value was decreased only after absorption of IgG and absorption tests using HBR-1 and MAK-absorbents showed a dramatic decrease in CEA value. These findings indicated the presence of IgG type human anti-mouse antibodies (HAMA), which interfered the measurement by AIA. Although we could not identify the reason why HAMA was produced in this patient, the facts that the false positive phenomenon was observed after the initiation of DCT and ALT, and that CEA value decreased after theses therapies were discontinued, indicated that immuno-modulaton by DCT and ALT may have a close relationship to HAMA production. It was probable that DCT and ALT activated preexisting heterophile-antibody-producing cells, which stimulated HAMA production. The incidence of such false positive reaction of CEA by HAMA in patients with DCT and ALT was low, but as the number of the patient with immuno-cell therapy increases, the incidence of such phenomenon surely increases. Because HAMA reacts to all types of immunoassay, careful attention should be paid to the evaluation of laboratory findings in patients undergoing with such immuno-cell therapies.