Rare tumour of the neuro-endocrine origin with generally non-aggressive behaviour, but have malignant potential depending on the site and size of the tumour.
About two-thirds are found within the gastrointestinal tract, including the small bowel, rectum, stomach, appendix and more rarely the liver and pancreas; a further quarter are found in the respiratory tract. Carcinoid tumours derive from a number of different neuroendocrine cells depending on the exact site of the tumour.
Some carcinoid tumours are associated with symptoms thought to be associated serotonin, higher levels of which are either due to secretion by the tumour or by altered tryptophan metabolism. Instead of oxidation to nicotinic acid, dietary tryptophan is 5-hydroxylated to produce 5-hydroxytryptophan, i.e. serotonin. Systemic release of excess serotonin is thought to be responsible for carcinoid syndrome (see also serotonin syndrome) and is more common with tumours within the mid-gut. However, the symptoms may be a result of secretion of other biologically active compounds including amines, tachykinins and other peptides as not all patients with high circulating serotonin experience symptoms. Carcinoid syndrome may include:
Cases where affected organs drain into the portovenous system rarely experience carcinoid syndrome as cell products are metabolised (via the monoamine oxidase pathway) by the liver. The kidney also has some capacity to metabolise serotonin. Where there are metastases to the liver or retroperitoneal disease, cases may be symptomatic.
- Type 1 (80% of cases) are developed in the context of chronic atrophic gastritis type A.
- Type 2 (10% of cases) are associated with Zollinger-Ellison syndrome and sometimes as part multiple endocrine neoplasia syndrome (MEN-1).
- Type 3 (10% of cases) are sporadic tumors without hypergastrinaemia.
May be found incidentally at appendicectomy when tissue sent to pathology. 5-HIAA (5-hydroxyindoleacetic acid) is the main metabolite of serotonin and tryptophan. Raised levels may be detected in the urine (normal range 2-8mg in 24 hours).
Serum chromogranin A has also been used in diagnosis, being more sensitive but at the expense of specificity.
Unless local invasion or distant metastases are seen, histological features alone cannot predictably distinguish between benign and malignant tumours.
Surgery is the only curative option.
Somatostatin antagonists may be used to supplement chemotherapy in malignant carcinoid and to control symptoms in otherwise benign tumours.
- ↑ Oberndorfer S. Karzinoide Rumoren des Dunndarms. Frankf Z Pathol 1907;1:425-9.
- ↑ Modlin IM, Lye KD, Kidd M. A 5-decade analysis of 13,715 carcinoid tumors. Cancer. 2003 Feb 15; 97(4):934-59.(Link to article – subscription may be required.)