COMPARISON OF COMPLETE VERSUS FRAGMENTED TC-99M-LABELED ANTI-CEA MONOCLONAL-ANTIBODIES FOR IMMUNOSCINTIGRAPHY IN COLORECTAL-CANCER

The goal of this study was to intraindividually compare complete versu s fragmented directly labeled Tc-99m monoclonal anti-CEA antibody with respect to antigen targeting and tumor uptake kinetics, sensitivity a nd diagnostic accuracy in colorectal cancer patients. Methods: Twenty- five patients were investigated with Tc-99m-labeled anti-CEA IgG(1) BW 431/26 and the F(ab')(2)/Fab' fragment mixture F023C5 within 7 days. For quantitative analysis, an ROI technique was applied to planar scan s, whole-body scans and SPECT slices 10 min to 48 hr postinjection. Fi nal correlations were performed according to histology after surgery o r biopsy. Results: Earliest tumor detection with complete IgG(1) was p ossible 4 hr postinjection (52% of finally positive lesions); imaging at 24 hr or even 48 hr was necessary in 48%. Tumor detection with frag ments was possible in 17% at 1 hr postinjection and in 94% at 4 hr pos tinjection. In 35%, SPECT was necessary for tumor detection with both MAbs. Absolute antibody uptake in tumor lesions was higher with comple te MAbs than with fragments. Conclusions: Lesions known for their good vascularization, vascular permeability and antigen accessibility were detected earlier and with higher sensitivity with fragments than with complete MAbs due to faster background clearance despite lower absolu te antibody uptake.