Localisation of gastrointestinal cancer with a 131 I labelled monoclonal antibody to CEA

The localisation of tumour deposits by a 131 I labelled monoclonal antibody to carcinoembryonic antigen (CEA) has been evaluated in 24 patients with primary gastric, oesophageal and colorectal cancer and in 26 patients with clinically suspected recurrent gastric and colorectal cancer. Seventeen of 20 primary sites and 6/15 associated secondary sites were correctly identified by external scanning. Measurement of radiolabelled antibody in the resected specimens demonstrated a 2.6-3.3 fold increase in comparison with the surrounding normal tissue (P less than 0.01). The antibody scans were compared with computerised tomography (CT) in the detection of recurrent disease. The respective sensitivities and specificities for the two investigations were 61% and 33% for antibody scanning and 64% and 100% for CT. Assessment of the distribution of labelled antibody demonstrated rapid clearance with less than 2% detectable in serum samples at 24 h. The implications of these findings together with the mechanisms of excretion are discussed.