Immunohistochemical evidence of peptide hormones in endocrine tumors of the rectum

Twenty‐five endocrine tumors of the rectum (rectal carcinoids) were examined immunohistochemically for various pancreatic and gut neurohormonal polypeptides. Twenty‐one of the tumors were found to contain cells displaying pancreatic polypeptide (PP), glucagon, somatostatin, insulin, substance P, enkephalin or β‐endorphin immunoreactivity. At least 11 of the tumors contained more than one peptide hormone. In some of the tumors PP cells made up the major cell population, in others the glucagon cells constituted the majority. Only four of the tumors contained 5‐hydroxytryptamine. Rectal endocrine tumors seem unique among gut endocrine tumors in that they may store immunoreactive enkephalin, β‐endorphin and even insulin. None of the patients displayed the carcinoid syndrome; symptoms were usually vague and uncharacteristic. In many cases the tumor was found at routine examination.