Monoclonal antibody imaging as an adjunct to radiographic CT in abdominal metastasis

In imaging over 50 patients with I-131 labeled F(ab')/sub 2/ fragments of monoclonal antibodies directed against colorectal carcinoma cell surface antigens the authors have identified 5 areas of potential utility for this diagnostic method to provide information complimentary to that provided by radiographic CT. Approximately 100-500 mg of F(ab')/sub 2/ fragments are labeled by the iodogen method with approximately 37 MBq (1 mCi) I-131. Intravenous administration to patients with known or suspected colorectal carcinoma is followed by daily imaging for up to 7 days. Patients also undergo radiographic CT scanning and either a CT-guided biopsy or surgical biopsy for pathology and immunoperoxidase staining for the colorectal antigen. Patients have been identified in 5 categories of diagnostic utility where the antibody images provided information beyond that available from CT: (1) Small disease: Lymph nodes normal in size (1 cm) on CT have been detected by antibody imaging. (2) Differentiation of post-operative change from recurrent tumor: Despite little change in soft tissue mass at the primary operative site on CT scans 3 months apart, antibody scan indicated recurrent tumor, confirmed at surgery. (3) Localization of recurrence in patients with no identifiable disease by CT but rising serum CEA. (4) Differentiation of types of tumor metastasis in patients with more than one, or unknown, primary. (5) Quantitative evaluation of localization of antibody in tumor, for therapeutic applications. While most sites of disease were localized by CT scans, they have identified five categories of additional information provided by the antibody scans that have influenced clinical decisions in these patients