gastrointestinal carcinoid tumor An indolent (slow-growing) cancer that forms in cells that make hormones in the lining of the gastrointestinal tract (the stomach and intestines). It usually occurs in the small intestine, rectum, or appendix (a small fingerlike pouch of the large intestine). Having gastrointestinal carcinoid tumor increases the risk of forming other cancers of the digestive system. |