Gastrointestinal neuroendocrine tumors (NETs) are the second most prevalent malignant type of gastrointestinal tumor in the U.S.. It is estimated that over 100,000 Americans are affected (1). NETs grow more slowly than other cancers of the GI tract. Once considered rare, the incidence of gastrointestinal neuroendocrine tumors is increasing. Early diagnosis, intervention, and control of symptoms are essential.
The gastrointestinal tract contains more neuroendocrine cells than any other system in the body. Neuroendocrine cells have the characteristics of nerve cells and hormone-prducing cells. In the GI tract, neurendocrine cells control the release of digestive juices and the rate at which food passes through (2).
Gastrointestinal neuroendocrine tumors are classified as pancreatic neuroendocrine tumors and carcinoid tumors.
Pancreatic neuroendocrine tumors originate within the pancreas and account for 5 percent of all pancreatic tumors. Pancreatic NETs are classified according to the hormone producing cell of origin. Half are identified as functioning because the tumor produces hormones, The remaining are classified as non-functioning because the tumor does not produce hormones.
Carcinoid refers to neuroendocrine tumors which develop in the stomach, intestines, appendix and rectum. It is the more common type of gastrointestinal neuroendocrine tumor. NETs secrete a variety of hormones. In most cases, the levels of hormones secreted by the tumor are not significant enough to produce symptoms. However, as the tumor grows and spreads, high amounts of hormones are released. About one in 10 individuals with carcinoid tumors will experience carcinoid syndrome. Symptoms of carcinoid syndrome are redness of the skin with a feeling of warmth, diarrhea, and a rapid heart rate (3).
Gastrointestinal neuroendocrine tumors are more common among Afro-Americans and women. Some individuals with a family history of neurofibromatosis type one develop NETs of the small intestines. It is estimated that inherited mutations of the MEN1 gene account for 10 percent of carcinoid tumors (2).
Diagnosis is made by biochemical monitoring and radiological imaging.