The localization of an anti-tumour monoclonal antibody (791T/36) in gastrointestinal tumours.

Fifty-six patients with gastrointestinal cancers and four patients with benign colorectal tumours have been injected with radiolabelled anti-tumour monoclonal antibody ( 791T /36) to assess the degree of localization of the antibody by external scintiscanning and measurements on resected specimens. Twenty-nine patients with primary colorectal cancer showed increased uptake of the radiolabelled antibody in the resected tumours, with a tumour to normal tissue (T:NT) ratio of 2.5:1. All but two of fifteen patients with recurrent or metastatic tumour showed positive images of the deposits on external scintiscanning. Twelve patients with noncolonic gastrointestinal malignancy were studied and in only two patients were tumours demonstrated by external scanning. There were no positive images in four patients with benign colonic disease nor could increased uptake of radiolabelled antibody be demonstrated in the resected specimens. Immunohistology and autoradiography have shown that the antibody can be demonstrated in the pseudoacini and stroma of colon cancer. There are indications that this may represent localization to a cell surface antigen which becomes detached in the processing of the histological sections. It seems that in the gastrointestinal tract the monoclonal antibody 791T /36 is consistently taken up by colorectal cancer. Only a few noncolonic cancers and no benign colonic tumours take up the antibody. This antibody uptake may prove of value in the detection of occult metastases and in the targeting of antitumour agents.