Carcinoid Tumors

Most carcinoid tumors arise in the GI tract (appendix, ileum, and rectum), but they can also be seen in the lungs and elsewhere. Carcinoid tumors are capable of secreting substances that affect vascular, bronchial, and GI smooth muscle tone. Serotonin and histamine are the most commonly secreted hormones, but carcinoid tumors are capable of secreting 35 peptides and hormones, including bradykinin, prostaglandins, kallikrein, and others. Stimuli for the release of mediators include catecholamines, histamine, hypotension, and tumor manipulation.