Incidental detection of carcinoid with Tc-99m-labeled carcinoembryonic antigen monoclonal antibody scintigraphy during evaluation of metastatic colon cancer

A 63-year-old man was referred for increasing carcinoembryonic antigen (CEA) levels 2 years after sigmoid resection for colon cancer. He reported fatigue, diarrhea, and tenesmus. A physical examination and laboratory evaluations were notable only for the abnormal CEA level of 24 pg/ml (normal, 0-5 pg/ml). Colonoscopy, chest radiograph, bone scan, and CT with contrast were unremarkable. Tc-99m CEA scintigraphy revealed an abnormality near the right kidney, which was later localized with a gamma probe and found to be carcinoid. Although both colorectal carcinoma and carcinoid may have a histogenetic relation to typically mucinous adenocarcinomas, produce CEA, and can occur concurrently (called 'collision tumors'), this is not well described with CEA scintigraphy. This is the first report of such a case found with a CEA scan.