DIAGNOSTIC-ACCURACY AND TUMOR-TARGETING KINETICS OF COMPLETE VERSUS FRAGMENTED TC-99M-LABELED ANTICARCINOEMBRYONIC ANTIGEN ANTIBODIES - AN INTRAINDIVIDUAL COMPARISON

The goal of this study was to intraindividually compare a complete ver sus a fragmented, directly Tc-99m-labeled, monoclonal anti-carcinoembr yonic antigen (CEA) antibody, with respect to their antigen-targeting kinetics, sensitivity, and diagnostic accuracy in patients with CEA-ex pressing tumors. Twenty-five patients were investigated with the Tc-99 m-labeled anti-CEA IgG1 BW 431/26 and the F(ab')(2)/Fab' fragment mixt ure F023C5 within 7 days, For quantitative analysis, the region of int erest technique was applied to planar scans, whole-body scans, and sin gle photon emission computed tomography slices 10 min to 48 h postinje ction (PI), Final correlations were performed according to the histopa thology after surgery or biopsy. Earliest tumor detection was possible with complete IgG1 4 h PI (52% of finally positive lesions). Twenty-f our- or even 48-h scans were necessary in 48% of finally positive lesi ons; tumor detection with fragments was possible in 17% at 1 h PI and in 94% at 4 h PI. With both monoclonal antibodies, in 35%, single phot on emission computed tomography was necessary for tumor detection, Abs olute antibody uptake in tumor lesions was higher with complete monocl onal antibodies than with fragments. The sensitivity of fragments was higher in detecting primary tumors, local recurrences, and lymph node metastases. For detection of liver metastases, sensitivity was also hi gher for fragments than for IgG (87 versus 73%), but in scintigraphica lly positive lesions, tumor:background ratios were significantly lower with fragments (1.26 +/- 0.12 versus 1.70 +/- 0.32; P < 0.01). Theref ore, fragments seem to be more suitable for earlier detection of lesio ns known for their good vascularization, vascular permeability, and an tigen accessibility, such as local recurrences, lymph node metastases, and peritoneal carcinomatoses. In liver metastases (high interstitial pressure, low vascular leakage), sensitivity of fragments is higher, but their rapid serum and whole-body clearance lead to a lower absolut e antibody uptake, with the consequence of significantly lower tumor:b ackground ratios than with IgG.