Table 3.

Classification of carcinoid neuroendocrine tumours [19, 20]

Origin	Carcinoid	Metastases	Organ	Clinical	Hormone
	syndrome	to bone		symptoms	production a
Foregut	May occur; usually in cases with liver metastases	Common	Thymus	Cushing’s syndrome, acromegaly	CRH, ACTH, GHRH (low 5-HT)
			Lung	Cushing’s syndrome, acromegaly	CRH, ACTH, GHRH, PP, hCG-alpha, neurotensin, 5-HTP, (low 5-HT), histamine
			Stomach	Cushing’s syndrome, pernicious anaemia acromegaly, ZES	CRH, ACTH, GHRH, gastrin
			Duodenum	Somatostatinoma syndrome, ZES	Gastrin, somatostatin, neurotensin, tachykinins, (low 5-HT)
Midgut ‘classical carcinoid’	Occurs frequently, in cases with metastases	Rare	Ileum	Carcinoid syndrome	Tachykinins, bradykinins, CGRP, high 5-HT
			Jejunum
			Proximal colon
			Appendix	Not hormone related	(Tachykinins, 5-HT)
Hindgut	Rare	Common	Distal colon	Not hormone related	PP, HCG-alpha, PYY, somatostatin (rarely 5-HT)
			Rectum

^a CRH, corticotrophin-releasing hormone; ACTH, adrenocorticotrophic hormone; GHRH, growth hormone-releasing hormone; PP, pancreatic polypeptide; hCG, human chorionic gonadotrophin; CGRP, calcitonin gene-related peptide; PYY, peptide YY; 5-HTP, 5-hydroxytryptophan; 5-HT, 5-hydroxytryptamine (serotonin).