Radioimmunoscintigraphy with 111In labelled monoclonal antibody fragments (F(ab')2 BW 431/31) against CEA: radiolabelling, antibody kinetics and distribution, findings in tumour and non-tumour patients.

Forty seven patients with suspected malignant disease (mainly colorectal cancer) were studied with 111In labelled F(ab')2 fragments of an anti-CEA monoclonal antibody (BW 431/31). The kinetic data revealed a long whole body retention of the label (62% after 4 days) and a rapid blood clearance (77% within 24 h, 89% within 48 h) leading to an early positive tumour contrast 24 h p.i. and optimal scintigrams 48 h p.i. Diagnostic results were promising in local recurrences of colorectal cancer (8/10 positive = 80%) though false positive findings in patients with inflammatory bowel disease occurred probably due to cross-reaction with a human granulocyte antigen. Liver metastases and tumours neighbouring liver and spleen were often missed (10/27 = 37%) because of high nonspecific uptake in these organs. Thus BW 431/31 proved to be a suitable compound for radioimmunodetection, however, further improvements to optimize tumour affinity and specificity of the antibody are mandatory.