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Carcinoid syndrome

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Carcinoid tumours describe a range of neoplasms arising from neuroendocrine cells or their precursors. Of intestinal carcinoids, the most common sites are in the midgut, especially the appendix and terminal ileum. Non-intestinal carcinoids include those of the lung, testes and ovary. They are usually of low-grade malignancy.

The carcinoid syndrome develops when products, chiefly serotonin, are released by the tumour in large amounts and escape hepatic degradation (1,2)

  • caused by the release of serotonin and other substances from well-differentiated neuroendocrine tumours (NETs)
  • hallmark symptoms of carcinoid syndrome are:
    • flushing and diarrhea
    • atypical signs and symptoms can include:
      • wheezing,
      • abdominal pain,
      • valvular heart disease,
      • telangiectasias, pellagra,
      • complications of mesenteric fibrosis, including ureteral obstruction, bowel obstruction, and bowel ischemia

  • symptoms are mediated by the release of serotonin (5-HT), histamine, kallikrein, prostaglandins, and tachykinins

Carcinoid syndrome:

  • is a paraneoplastic syndrome associated with the secretion of approximately 40 vasoactive hormones, predominantly 5-hydroxytryptamine (5-HT) (1)
    • also involves the secretion of histamine (primary gastric NETs), kallikrein, prostaglandins E and F, and tachykinins
    • NETs can arise in the foregut, midgut, or hindgut

The carcinoid syndrome is seen in two situations:

  • intestinal carcinoids with hepatic metastases:
    • the metastases reach sizes several times larger than that of the primary tumour and secrete products into the hepatic vein
    • the vasoactive tumour products are able to enter the systemic circulation
  • extra-intestinal carcinoids

Epidemiological studies from the US suggest the age-adjusted incidence of carcinoid tumours varies between 2.47 and 4.48 per 100,000 population, with the rates being highest in black males, then black females, then white Americans (1)

  • population corrected male-to-female ratio for all carcinoid sites was 0.86
  • average age at diagnosis for all carcinoid tumours was 61.4 years (compared with 63.9 years for non-carcinoid tumours)


  • requires these symptoms and corresponding elevations in lab tests

Treatment options include surgery and medical management with somatostatin analogs


  1. Endocr Relat Cancer. 2004 Mar;11(1):1-18.
  2. Gade AK, Olariu E, Douthit NT. Carcinoid Syndrome: A Review. Cureus. 2020 Mar 5;12(3):e7186. doi: 10.7759/cureus.7186.

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