Gastrointestinal carcinoid tumors form in the lining of the gastrointestinal tract, which includes the stomach, small intestine, colon and rectum. Approximately 8,000 of those cases are diagnosed each year in the United States, according to the American Cancer Society.
How gastrointestinal carcinoid tumors develop
Gastrointestinal (GI) carcinoid tumors start in the neuroendocrine system, which is made up of cells that resemble nerve cells and hormone-making cells in the gastrointestinal tract. These cells control the production of digestive juices and the muscles that guide food and waste through the stomach and intestines. Cells in this system are not concentrated in a particular organ; they are found in several areas of the body but tend to be concentrated in the gastrointestinal (GI) tract.
Like other types of cancer, GI carcinoid tumors form when abnormal neuroendocrine cells grow uncontrollably, joining together to form a growth called a tumor. GI carcinoid tumors are rare and grow very slowly.