Carcinoid syndrome

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)

Diagnosis

• requires these symptoms and corresponding elevations in lab tests

Treatment options include surgery and medical management with somatostatin analogs

Reference:

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.