99Tcm-IMMU4 imaging in recurrent colorectal cancer: efficacy and impact on surgical management.

The aims of this study were to evaluate the efficacy of scintigraphy with the 99Tcm-labelled anti-carcinoembryonic antigen (CEA) monoclonal antibody Fab' fragment (IMMU4) in the diagnosis of recurrent colorectal carcinoma and to investigate its usefulness in the intraoperative surgical management of patients undergoing re-operation because of a rising serum CEA. We evaluated 24 patients prospectively who had rising serum CEA 6-19 months after initial surgery for colorectal carcinoma. Ten patients had lesions confirmed by computed tomography, ultrasound, magnetic resonance imaging, endoscopic examination or barium enema. Fourteen patients had negative findings on one or more of the above studies, but were suspected of having occult disease from their rising serum CEA. All patients were scheduled for surgery for restaging during a "second look' procedure. Planar and single photon emission tomography (SPET) imaging was performed in all patients. All scintigraphic findings were correlated with surgical and histopathological results. The overall sensitivity, specificity and accuracy were 81, 90 and 86% respectively when analysed by lesion, and 95, 60 and 88% respectively when analysed by patient. Ten of 14 (71%) patients with occult disease were correctly diagnosed as having recurrent disease. The SPET images were shown to have superior detectability (80%) compared with the planar images (35%). The surgeon judged the study to have had a neutral impact in 75% of the patients, but to have been helpful in 25%. We conclude that this antibody is potentially useful in detecting recurrent colorectal carcinoma in patients with rising serum CEA, especially when conventional imaging is negative or equivocal. It can also be helpful in altering planned surgery.