In-111 CYT-103 monoclonal antibody imaging in patients with suspected recurrent colorectal cancer.

Recurrent colorectal cancer is seen in as many as 40% of patients after curative resection. In view of the limitations of endoscopic and cross-sectional imaging, external immunoscintigraphy has been added to the follow-up regimen of patients at high-risk of recurrent disease. The authors investigated the utility of immunoscintigraphy with Indium-111 (In-111) CYT-103 (site specifically labeled conjugate of monoclonal antibody B72.3) in 19 patients with suspected recurrences after previous curative resection of colorectal carcinoma. Local or regional recurrences (4 patients) and liver metastasis (6 patients) were indicated by physical examination and computed tomography (CT), whereas nine patients had occult disease with increasing serum carcinoembryonic antigen (CEA) levels and negative conventional workups. Serum CEA levels were elevated (mean, 22 ng/ml) in all patients. Approximately 4.3 mCi In-111 labeled to 1.0 mg CYT-103 was administered intravenously to each patient. Planar and single photon emission computed tomography (SPECT) imaging were performed 2-5 days after infusion. The final diagnosis of recurrence or metastasis was established in 18 patients by second-look surgery or biopsy. One patient died before exploration. Tumor was identified at the following locations: pelvis (12 patients), abdominal wall (2 patients), retroperitoneum (1 patient), liver (5 patients), and omentum (2 patients). Superiority of monoclonal antibody (MoAb) scan is noted in the detection of pelvic and intraabdominal recurrences (100%) versus CT scan (43%). Liver metastases were identified with equal facility by both modalities. In-111 CYT-103 scan findings influenced the management of 10 (55%) of 18 patients. Surgery was avoided in one patient with disseminated metastases detected by the scan. Correct identification of occult local recurrences was made in six patients. An isolated liver metastasis was confirmed in one patient with equivocal CT scan. Finally, additional intraabdominal lesions were detected in two patients. These results suggest an important and beneficial role for In-111 CYT-103 MoAb imaging in patients with suspected recurrent colorectal carcinomas, particularly in patients in whom cross-sectional imaging is negative; such imaging may prevent patients from undergoing unnecessary surgical exploration.