VALUE OF RADIOIMMUNOSCINTIGRAPHY WITH TC-99M LABELED ANTI-CEA MONOCLONAL-ANTIBODY (BW431 26) IN THE DETECTION OF COLORECTAL-CANCER/

This study was undertaken as part of a Coordinated Research Programme initiated by the International Atomic Energy Agency to evaluate the us efulness of radioimmunoscintigraphy (RIS) in the management of patient s with colorectal cancer. Technetium-99m labelled BW431/26, a monoclon al antibody against carcinoembryonic antigen (CEA), was used. The stud y included 73 patients (31 females and 42 males), Sixty-eight patients were suspected of having recurrent colorectal adenocarcinoma while an other five were suspected to have primary colorectal cancer. Images we re acquired at 10 min and 4 and 24 h following the injection of radioa ntibody. The efficacy of RIS in tumour detection was evaluated by the findings at surgery, histological investigation and/or other diagnosti c modalities and clinical follow-up. Four of five patients with suspec ted primary colorectal cancer gave true-positive results (three at pri mary sites, one at the site of a metastatic lesion) while one was fals e-positive. The overall accuracy of RIS in the diagnosis of recurrent colorectal cancer was 87%. Its sensitivity in the detection of locoreg ional or abdominal recurrence and liver metastases was 97% and 89% res pectively. RIS was more accurate than computed tomography (CT) scan in the detection of pelvic recurrence and liver metastases while CT scan was far superior to RIS in detecting lung metastases. RIS proved most useful in patents who had rising CEA levels on clinical follow-up but in whom other work-up, including CT scan, was negative. The advantage s of RIS include the ability to detect tumour recurrence prior to othe r investigations and to identify tumour recurrence in areas such as th e pelvis, where CT and magnetic resonance imaging have their greatest weaknesses in diagnosing recurrent disease. The imaging accuracy is si gnificantly increased when combined CT and antibody imaging is perform ed.