Comparison of complete versus fragmented technetium-99m-labeled anti-CEA monoclonal antibodies for immunoscintigraphy in colorectal cancer.

Unlabelled: The goal of this study was to intraindividually compare complete versus fragmented directly labeled 99mTc monoclonal anti-CEA antibody with respect to antigen targeting and tumor uptake kinetics, sensitivity and diagnostic accuracy in colorectal cancer patients.

Methods: Twenty-five patients were investigated with 99mTc-labeled anti-CEA IgG1 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 scans, whole-body scans and SPECT slices 10 min to 48 hr postinjection. Final correlations were performed according to histology after surgery or biopsy.

Results: Earliest tumor detection with complete IgG1 was possible 4 hr postinjection (52% of finally positive lesions); imaging at 24 hr or even 48 hr was necessary in 48%. Tumor detection with fragments was possible in 17% at 1 hr postinjection and in 94% at 4 hr postinjection. In 35%, SPECT was necessary for tumor detection with both MAbs. Absolute antibody uptake in tumor lesions was higher with complete 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 absolute antibody uptake.