Evaluation of immunolocalization in gastrointestinal cancer

Tumor localization by a 131I-labeled monoclonal antibody to CEA has been evaluated in a series of 50 patients with clinically suspected primary or recurrent gastrointestinal cancer. Eighty-five percent of the primary tumors were correctly detected, as were 43% of associated nodal metastases. Localization was compared with computerized tomography in the detection of recurrent disease. Each technique correctly identified 61% of the sites but missed 39%. In addition, labeled antibody localization produced a significant number of false-positive images. Radioactivity accumulated by tumors, both primary and secondary, was significantly higher than that in surrounding normal tissue (P less than .01). However, less than 0.8% of the injected radioactivity and 0.01% of the injected antibody were detectable in the tumors. Radiolabeled antibody was rapidly cleared from the circulation, and this may reflect a recipient reaction to the foreign protein.