Radiolabeled Antibodies for the Detection of Cancer: New Approaches to Improve the Sensitivity and Specificity of Immunoscintigraphy

Paul Ehrlich’s concept of “magic bullet” for the cure of diseases has been revitalized by the development of the monoclonal antibody (Mab) technology allowing the production in unlimited amounts of antibodies of perfect homogeneity and specificity directed against various tumor markers. This chapter will review one aspect of the magic bullet concept, the use of radiolabeled antibodies as tracer for tumor detection by immunoscintigraphy. We shall critically consider the results obtained in this attractive field, from our early experimental results with 131I labeled polyclonal antibodies against carcinoembryonic antigen (CEA) up to the most recent clinical results obtained with 123I labeled fragments of anti-CEA Mab. Special emphasis will be given to the difficulties encountered in the detection of liver metastases when using intact anti-CEA antibodies and to the improvement obtained when we used 123I labeled Mab fragments and single photon emisssion computerized tomography (SPECT) for their localization in three dimensions.