Carcinoid tumors are slow-growing malignancies (cancerous growths) that usually occur in the ileum (the lower section of the small intestine), the appendix, and the rectum. These tumors secrete large amounts of normal body chemicals such as serotonin, bradykinin, histamine, and prostaglandins.
https://my.clevelandclinic.org/health/diseases/16831-carcinoid-syndrome

