Carcinoid tumours

Carcinoid tumours are neuroendocrine tumours. The majority (55%) are found in the GI tract with the commonest location being the small intestine, especially the ileum (note that previously the appendix was thought to be the commonest location). A further 30% of carcinoid tumours are found in the lungs.

They primarily secrete serotonin (5HT) but may also produce other substances.

They are classically associated with carcinoid syndrome, features of which include:
  • Flushing – this may be provoked by foods such as bananas, tomatos, kiwi or cheese, or by alcohol or exercise
  • Diarrhoea
  • Bronchospasm
  • Hypotension
  • Pellagra – due to both serotonin and niacin needing tryptophan as a precursor
  • Right-sided heart disease – especially fibrosis of the tricuspid valve.

However, note that to get carcinoid syndrome serotonin must reach the circulation. Since the liver metabolises serotonin, carcinoid syndrome will only occur if there is liver involvement or the tumour is in a location whereby the circulation can bypass the liver – for example the foregut.

Complications of carcinoid tumours include appendicitis, obstruction or intussception.

Diagnosis of carcinoid tumours is by:
  1. 24hr urinary 5-HIAA (which is a metabolite of serotonin) – only positive if it is a secretory tumour
  2. plasma chromograffin
Treatment of carcinoid tumours is:
  • surgery
  • ocreotide = somatostatin analogue

If these tumours are over-handled during surgery or out-grow their blood supply, a massive 'hormone hit' can be released in one go, causing a carcinoid crisis.

Features of a carcinoid crisis:
  • vasodilation
  • hypotension
  • tachycardia
  • bronchoconstriction
  • hyperglycaemia
This must be treated with an infusion of ocreotide.

5 yr survival for patients with small bowel carcinoid is around 60%
Patients with carcinoid heart disease have a worse prognosis.

Small print gems: False elevation of urinary 5-HIAA can occur in coeliac sprue, Whipples disease SBO and if the patient eats avocados, bananas or walnuts. False elevation of plasma chromogranin can occur in liver/renal failure, IBD, multiple myeloma and chronic PPI use.

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