A gastrointestinal (GI) carcinoid tumor is a slow-growing tumor that forms in the neuroendocrine cells in the GI tract. The GI tract includes the stomach, small intestine, colon, rectum, appendix, and other organs. Most GI carcinoid tumors form in the rectum, small intestine, or appendix.
GI carcinoid tumors are a type of neuroendocrine tumor. Neuroendocrine cells release hormones into the blood when they receive a signal from the nervous system. The type of hormone released depends on where the tumor is found in the GI tract.
People who have a family history of multiple endocrine neoplasia type 1 (MEN1) syndrome or neurofibromatosis type 1 (NF1) syndrome have a higher risk of GI carcinoid tumors.