What are carcinoid tumours?

Carcinoid tumours are tumours derived from neuroendocrine cells, primarily of the gut, but also from other tissues. They develop from 'apud' (amine precursor, uptake and decarboxylation) cells. These are cells with a common embryological origin which take up chemicals called amines (such as tryptophan), converting them by a series of chemical reactions into a variety of different active hormones.

The main locations of these tumours are:

Gastrointestinal tract (85%):

  • Foregut - stomach, beginning of duodenum, bile ducts and pancreas
  • Midgut - end of duodenum, jejunum, ileum, appendix, ascending colon
  • Hindgut - transverse colon, descending colon, sigmoid colon, rectum
These are illustrated in the diagram below

Diagram summarising tumour location

Diagram summarising tumour location - click to enlarge

Bronchus (10%)

The large airways.

Other (5%)

Gonads, kidney, breast, thymus, skin.

The tumours secrete a variety of hormones that cause the symptoms including:

  • serotonin
  • kinins
  • histamine
  • prostaglandins
  • catecholamines
  • neurotensin
  • substance P


The majority of carcinoid tumours are benign but all are potentially malignant if left long enough. Common sites of spread include the liver, lung and bone but reports exist of secondary tumours in almost every organ. Even if the tumour is malignant, it does not appear to be very aggressive, with survival after diagnosis of up to 20 years.