DETECTION OF PSEUDOMYXOMA PERITONEI BY RADIOIMMUNOHISTOCHEMISTRY AND RADIOIMMUNOSCINTIGRAPHY

Pseudomyxoma peritonei (PP) is a local slowly progressing disease with typical abdominal swelling. Treatment is uneffective and the long-ter m prognosis is poor. Conventional radiology provides usually only a de lineation of low density area relating gelatinous masses accumulating in the peritoneal cavity. In this study, immunohistochemistry based on digital quantitative autoradiography utilizing radiolabelled monoclon al antibody B72.3 (MoAb) recognizing TAG-72 antigen on epithelial carc inomas was used for diagnosis of pseudomyxoma (7 patients). The PP pat ients were studied with radioiodinated I-131-labeled MoAb after intrav enous (2 patients) and intraperitoneal (7 patients) injections. Radioa ctivities of MoAbs varied considerably in the tumours. Both intra- and extracellular staining pattern was observed by immunohistochemistry. Gamma imaging at 1,3, 7 and 14 days after i.v. injection (2 patients) revealed targeting of all known lesions. The intraperitoneally injecte d MoAb (7 patients) retained long time in the peritoneal cavity, speci fic tumour targeting was seen up to 16 days by an antibody-SPECT, whil e maximum blood radioactivity was measured between 8-12 hrs. Radiolabe lled B72.3 MoAb recognizing TAG-72 antigen is also present within pseu domyxoma cells. It can be used for radioimmunohistochemistry of PP. Ac curate imaging of PP is possible by MoAb suggesting earlier diagnosis and more accurate location of residual disease after operations, and e valuating treatment reponse. Estimated tumour dose for intraperitoneal tumour (MIRD formalism) was 13 mGy/MBq. This indicates that the radio iodinated B72.3 antibody can be used for in vivo targeting and therape utic applications of intraperitoneal pseudomyxoma.