FDG PET and immunoscintigraphy with 99mTc-labeled antibody fragments for detection of the recurrence of colorectal carcinoma.

Unlabelled: The aim of this study was to compare FDG PET with a new monoclonal antibody-based imaging agent that comprises an anti-carcinoembryonic antigen (CEA) monoclonal antibody Fab' fragment directly labeled with 99mTc.

Methods: Twenty-eight patients who were previously treated for colorectal carcinoma and in whom recurrence was suspected were examined with FDG PET and immunoscintigraphy. The most common indications were an elevation of serum CEA (13 patients), suggestive lesions documented by CT (9 patients), sonography (4 patients), and severe constipation (2 patients). Planar imaging and SPECT were performed 4-6 h after intravenous injection of the new imaging agent. Whole-body PET was performed 45-60 min after intravenous injection of FDG. The findings were confirmed by conventional diagnostic modalities, surgery, and histology.

Results: Histology confirmed local tumor recurrence in 9 of 28 patients. Clinical follow-up or CT confirmed the presence of liver metastases in 9 patients and lymph node involvement, lung metastases, and bone metastases in 2 patients each. The new agent correctly detected 8 of 9 local recurrences, whereas FDG PET was able to detect all 9 cases and in 1 case was false-positive. Liver metastases were confirmed in 9 patients by FDG PET but in only 1 patient by the new agent. Two cases with lymph node metastases and 2 cases with lung metastases were correctly identified by FDG PET, but none were detected by the new agent. Finally, bone metastases were identified in 1 patient by FDG PET but not with the new agent, whereas bone marrow infiltration (n = 1) was diagnosed by both imaging modalities.

Conclusion: These results indicate that FDG PET and 99mTc-labeled anti-CEA Fab' are suitable for the diagnosis of local recurrence of colorectal carcinoma but that FDG PET is clearly superior in the detection of distant metastases (liver, bone, and lung) and lymph node involvement.