Improved tumour localisation using indium-111 labelled antibodies.

Immunoglobulin G (IgG) antibodies to carcinoembryonic antigen (CEA) were labelled with radioactive indium (111In) or iodine (131I) and a comparison made of their value in locating CEA producing tumours. Eleven patients given 111In-anti-CEA had 31 tumours as judged by a combination of all techniques. Of these, 28 were detected by 111In-anti-CEA and 26 by conventional clinical techniques. Five of the patients also received 131I-anti-CEA. These patients had 15 tumour areas. Thirteen were detected by 111In and eight by 131I. 111In also produced a better signal to noise ratio in the scans and thereby showed lesions with greater certainty. In addition, the 111In isotope continued to accumulate in the tumour areas for considerably longer than 131I. Absorbed doses (whole body) were similar for both isotopes. The results show that antibody scanning is greatly improved by using 111In as the radiolabel in place of 131I and should allow the detection of smaller or deeper lesions.