Impact of radiolabeled antibody imaging on management of colon cancer.

One hundred patients with known or suspected colorectal cancer were studied by radioimmunoconjugate scintigraphy prior to operation. Study subjects received murine monoclonal anticarcinoembryonic antigen labeled with indium 111 (Indacea). Sensitivity of imaging was 76 percent for primary tumors, 44 percent for hepatic metastases, 38 percent for extrahepatic abdominal metastases, and 78 percent for extraabdominal metastases. Seventeen of 46 patients (37 percent) with known or suspected hepatic metastases and no evidence of extrahepatic disease by conventional imaging methods had extrahepatic metastases at exploratory surgery. Nine of the 17 patients had disease accurately predicted by the Indacea scanning. The management of each of these nine patients was, or could have been, modified by the scan findings and unnecessary surgery eliminated. A number of patients without post-operative disease had an unexplained increase in plasma carcinoembryonic antigen level due to production of human antimouse antibody. The addition of excess mouse immunoglobulin to the plasma prior to assay blocked this artifactual increase.