Utilisation en tomoscintigraphie d'anticorps monoclonaux radio-marqués pour la détection chez l'homme des cancers digestifs et des cancers médullaires de la thyroïde

Two 131-Iodine radiolabelled monoclonal antibodies were used to perform tomoscintigraphy in 42 patients: 11 patients bearing medullary thyroid cancers and 19 patients bearing gastrointestinal cancers received an antibody directed against carcino-embryonic antigen; 12 patients bearing gastro-intestinal cancers received an antibody directed against a non circulating antigen expressed by human colorectal cancers cell lines. Tomoscintigraphy is particularly useful for analysing the complex biodistribution of radiolabelled antibodies and the low contrast images encountered in immunoscintigraphy; the problems related to the true positive rate and to the clinical specificity of the method are discussed.

Immunoscintigraphie avec tomographie d'émission dans les cancers de la thyroïde

Immunoscintigraphy (IS) consists of in vivo body structure imaging using a specific labelled antibody to an antigen concentrated in the structure under study. Technically, the image contrast is better when IS is performed with a computerized emission tomography system. High concentrations of carcinoembryonic antigen (CEA) have been reported in medullary thyroid carcinoma and thyroglobulin (Tg) is a marker for differentiated thyroid carcinoma. We used injections of 131-I labelled monoclonal antibodies to CEA and Tg to detect thyroid tumours. A feasibility trial using anti-CEA antibodies gave very encouraging results. However, only tumours larger than 10 cm3 could be detected. Contradictory results were obtained using anti-Tg antibodies but this data must be considered as preliminary. Various means of improving the method and the concept of accessibility of the antigen to the antibody in vivo are discussed. This study shows IS to be a promising experimental technique. Further studies are required to define its clinical indications before it can be advocated for routine use.