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Neuroendocrine tumor refers to the type of cell that a tumor grows from rather than where that tumor is located. Neuroendocrine cells produce hormones or regulatory proteins, and so tumors of these cells usually have symptoms that are related to the specific hormones that they produce.
Neuroendocrine cells have roles both in the endocrine system and the nervous system. They produce and secrete a variety of regulatory hormones, or neuropeptides, which include neurotransmitters and growth factors. When these cells become cancerous, they grow and overproduce their specific neuropeptide. Neuroendocrine tumors are generally rare. One type of neuroendocrine tumor is a carcinoid tumor. This type of tumor can occur in the intestinal tract, appendix, rectum, bronchial tubes, or ovary. Most carcinoid tumors secrete serotonin. When the blood concentration of this hormone is high enough, it causes carcinoid syndrome. This syndrome refers to a variety of symptoms that are caused by the excessive amount of hormone secreted rather than the tumor itself.
The total incidence of neuroendocrine tumors is thought to be between five and nine million people in the United States. It is possible that these tumors are underreported because they grow slowly and do not always produce dramatic symptoms.
Causes and symptoms
Many of the symptoms of carcinoid tumor are due to the hormones that the tumor secretes. These hormones can affect the whole body and cause what is referred to as carcinoid syndrome. The most common symptom of carcinoid syndrome is flushing, a sudden appearance of redness and warmth in the face and neck that can last from minutes to hours. Other symptoms of carcinoid syndrome are diarrhea, asthma-like symptoms and heart problems. Since most carcinoid tumors are found in the appendix, the symptoms are often similar to appendicitis, primarily pain in the abdomen. When these tumors are found in the small intestine, they can cause abdominal pain that is often initially diagnosed as bowel obstruction. Many patients have no symptoms and the carcinoids are found during routine endoscopy of the intestines.
The diagnosis of carcinoid syndrome is made by the measurement of 5-hydroxy indole acetic acid (5-HIAA) in the urine. 5-HIAA is a breakdown (waste) product of serotonin. If the syndrome is diagnosed, the presence of carcinoid tumor is a given. When the syndrome is not present, diagnosis may be delayed, due to the vague symptoms present. Diagnosis can sometimes take up to two years. It is made by performing a number of tests, and the specific test used depends on the tumor's suspected location. The tests that may be performed include gastrointestinal endoscopy, chest x ray, computed tomography scan (CT scan), magnetic resonance imaging, or ultrasound. A biopsy of the tumor is performed for diagnosis. A variety of hormones can be measured in the blood as well to indicate the presence of a carcinoid.
The only effective treatment for carcinoid tumor as of the early 2000s is surgical removal of the tumor. Although chemotherapy is sometimes used when metastasis has occurred, it is rarely effective. The treatment for carcinoid syndrome is typically meant to decrease the severity of symptoms. Patients should avoid stress as well as foods that bring on the syndrome. Some medications can be given for symptomatic relief; for example, tumors of the gastro-intestinal tract may be treated with octreotide (Sandostatin) or lanreotide (Somatuline) to relieve such symptoms as diarrhea and flushing. These drugs are known as somatostatin analogs.
Liver transplantation is a treatment option for patients with neuroendocrine tumors that have metastasized only to the liver. As of 2004, this approach is reported to offer patients long disease-free periods and relief of symptoms.
The prognosis of carcinoid tumors is related to the specific growth patterns of that tumor, as well as its location. For example, a group of researchers at the University of Wisconsin reported in 2004 that patients with gastrointestinal tumors in the hindgut had longer periods of disease-free survival than those with foregut or midgut cancers. For localized disease the five-year survival rate can be 94%, whereas for patients where metastasis has occurred, the average five-year survival rate is 18%. It is not unusual for patients with carcinoid tumors to live ten or fifteen years after the initial diagnosis.
Neuroendocrine tumors such as carcinoid tumors are rare, and no information consequently is yet available on cause or prevention.
Beers, Mark H., MD, and Robert Berkow, MD., editors. "Carcinoid Tumors." Section 2, Chapter 17 In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
Ahlman, H., S. Friman, C. Cahli, et al. "Liver Transplantation for Treatment of Metastatic Neuroendocrine Tumors." Annals of the New York Academy of Sciences 1014 (April 2004): 265-269.
Oberg, K., L. Kvols, M. Caplin, et al. "Consensus Report on the Use of Somatostatin Analogs for the Management of Neuroendocrine Tumors of the Gastroenteropancreatic System." Annals of Oncology 15 (June 2004): 966-973.
Singhal, Hemant, MD, and Alan A. Saber, MD. "Carcinoid Tumor, Intestinal." eMedicine April 13, 2004. http://www.emedicine.com/med/topic271.htm.
Van Gompel, J. J., R. S. Sippel, T. F. Warner, and H. Chen. "Gastrointestinal Carcinoid Tumors: Factors That Predict Outcome." World Journal of Surgery 28 (April 2004): 387-392.
Carcinoid Cancer Foundation, Inc. 1751 York Ave., New York, NY 10128. (212) 722-3132. http://www.carcinoid.org.
Appendicitis — Inflammation of the appendix.
Growth factor — A local hormone produced by some cells that initiates growth.
Metastasis — The spread of disease from one part of the body to another, as when cancer cells appear in parts of the body remote from the site of the primary tumor.
Neurotransmitter — A chemical messenger used to transmit information in the nervous system.