Immunoscintigraphy of colorectal cancer using a monoclonal antibody 77-1

The monoclonal antibody (mAb) 77-1 recognizes epithelial membrane antigen (EMA) expressed by the majority of colorectal cancers. Following administration of indium-111 labelled 77-1, gamma camera imaging was carried out on 16 patients with known or suspected colorectal cancer prior to surgery or endoscopic laser therapy. Fourteen of the patients were found to have cancer, with one patient having two primary lesions. Two patients suspected of tumour recurrence were not found to have a lesion at laparotomy. Imaging before operation or laser therapy detected 10 out of 15 lesions (67%). Tumours which produced positive images were found to express the target antigen on immunocytochemical staining of the excised tumours. A mean tumour to normal colon ratio of 1.63 +/- S.D. 0.46 and a mean tumour to blood ratio of 3.60 +/- 1.48 were found at day 6 after antibody administration. A high uptake of radiolabel by the liver prevented the detection of hepatic metastases, present in three patients. Of the two patients with suspected recurrence a false positive scan was found in one owing to the presence of inflammatory tissue. Indium-111 labelled 77-1 may have a role in the imaging or targeting of colorectal cancer.