Contribution of SPECT to imaging of gastrointestinal adenocarcinoma with 111In-labeled anti-CEA monoclonal antibody.

Fourteen patients with suspected adenocarcinoma of the gastrointestinal tract received 1 mg of 111In-labeled anticarcinoembryonic antigen monoclonal antibody type ZCE025 combined with 40 mg unlabeled antibody of the same type. Planar and single-photon emission CT (SPECT) imaging studies were performed 3 days after infusion and, when possible, 7 days after infusion. Scan findings were correlated with the findings at surgery when possible. Tumor was detected by day-3 planar imaging in eight of 13 patients in whom tumor was documented histopathologically. Day-3 SPECT allowed demonstration of tumor in 11 of these 13 patients. In another patient whose scan was negative, no residual tumor was found at surgery. SPECT was particularly helpful in identifying small and midline tumors. In two cases, localization on SPECT helped identify the tumor mass on CT. Two primary tumors weighing less than 5 g could not be detected on either planar or SPECT scans. Histologically positive, normal-sized lymph nodes were not seen by planar imaging or SPECT. SPECT increased the detection rate over that achieved with planar imaging, helped to better localize scan abnormalities, and afforded more useful comparison between the monoclonal antibody study and CT.