Rectal and colonic carcinoids. A clinicopathologic study of 84 cases.

Eighty-four carcinoids of the colon and rectum were studied with emphasis on prognostic features, immunohistochemical characteristics, and pitfalls in diagnosis. Follow-up data were available on 35 patients. Tumors with adenocarcinomatous components, or those resembling small cell carcinomas of the lung, were excluded. Eighty-one tumors were in the rectum and three tumors were in the distal sigmoid colon. Neuron-specific enolase, chromogranin, and Leu-7 were positive in 87%, 58%, and 53% of the tumors, respectively. Hormones were positive in the following percentages: serotonin, 45%; pancreatic polypeptide, 46%; glucagon, 10%; gastrin, 3%; somatostatin, 3%; adrenocorticotrophic hormone, 1%; cholecystokinin, 0%; calcitonin, 0%; and insulin, 0%. Many tumors elaborated more than one hormone. Fifty-five percent of the tumors were argyrophil and 28% were argentaffin. Carcinoembryonic antigen was present in 24% of the tumors; 82% of the tumors contained prostatic acid phosphatase. Three patients had liver metastases; their tumors ulcerated, invaded muscularis propria, and had more than 2 mitoses per 10 high-power fields (HPF). One patient with a 2.5-cm tumor without mitoses had regional lymph node metastases. All non-metastasizing tumors had less than one mitosis in 10 HPF. We conclude that large bowel carcinoid tumors are essentially limited to the rectum and sigmoid, that they are indolent if mitotically inactive and smaller than 2 cm, and that most show production of a selected group of endocrine markers.