Definition	NET of enterochromaffin (EC-cells) of GI-tract, often secreting serotonin : forgut NET: pancreas - stomach - duodenum - jejunum - respiratory tract - thymus; midgut NET: ileum - appendix; hindgut NET: colorectal, urogenital tract
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Incidence	up to 15 per 1 Mill per year / ~ 50 % of all GEP-NET
Pathology - Pathophysiology	- most frequent NET of the GEP-system; up to 75% of all carcinoids are present as ileal carcinoids; pancreatic carcinoids are rare tumors - often all neuroendocrine GEP-tumors and islet-cell tumors are being referred to as "carcinoids" due to histological similarities and according to older classifications (see WHO-Classification) - pancreatic carcinoids expressing / secreting serotonin, often associated with an atypical Carcinoid-Syndrome are classified as true "SEROTONINOMA" . possible tumorigenesis: mutations of tumor-suppressor-gene (MEN-1-gene, menin-gene) discussed in MEN-1 patients, p53-tumo-rsuppressor-gene Carcinoids of the stomach frequent in genetic disposition (pernicious anemia, chron. atrophic gastritis, hypergastrinemia, hyperplasia of gastrin-producing cells (ECL-system) and in Zollinger-Ellison-Syndrome (Gastrinoma) symptoms due to serotonin and other vasoactive peptides; serotonin stimulates gastrointestinal motility and secretion; proliferation of fibroblasts
Clinical	typical clinical syndrome in up to 50 % of all carcinoids 1. flush (kinins: kallikrein, bradykinin) 2. secretory diarrhea (serotonin) 3. abdominal pain 4. endocardial fibrosis (lesions, valvular stenosis, arrhythmia) other symptoms: bronchial constriction, asthmatic attacks
Diagnosis	Laboratory: plasma serotonin concentration highly variable: (normal ~ 100 - 300 ng/ml ) / 24 hr excretion of 5-HIAA (metabolite) in acidified urin (normal < 10 mg/ day) variable; dependent upon nutrition (5-hydroxy-tryptamine: walnut, avocado, banana, pineapple), dep. upon medical drugs (phenothiazine, serotonin antagonists) Differential diagnosis: flushing without HIAA caused by menopause, alcohol, medical drugs, systemic mastocytosis, vipoma HIAA-excretion elevated in malabsorption syndromes (M.Whipple - sprue - celiac diseaes) Imaging of pimary tumor / metastases by means of octreotid scan OCTREOSCAN (somatostatin-receptor-szintigraphy), CAT scan, NMR, endoscopic sonography)
Therapy-Strategies	surgical resection - liver surgery (metastasectomy), lymph node surgery embolisation of liver metastases (transarterial), combination with chemotherapy - somatostatin analogs (Octreotide) interferon: alpha-interferon (IFN) system. chemotherapy radionuclid therapy, radiopeptide therapy (DOTATOC): Indium111 or Yttrium90 coupling (DOTA, DTPA) to synthetic somatostatin analog

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