Somatostatinoma

Somatostatinoma is a rare neuroendocrine tumour of delta cells, about 1 percent of gastroenteropancreatic endocrine neoplasms, most often in the duodenum followed by the pancreas; it may be sporadic or associated with neurofibromatosis type 1, MEN1 and von Hippel-Lindau disease, and functional tumours cause the inhibitory syndrome of mild diabetes, cholelithiasis and diarrhoea or steatorrhoea by suppressing gallbladder motility and endocrine and exocrine secretion, while non-functional tumours are asymptomatic or obstructive (J Gastroenterol Hepatol 2008). The incidence is about 1 in 40 million; duodenal and periampullary tumours cause jaundice or pancreatitis, and the NF1 association reflects RAS-MAPK pathway dysfunction, with the Pacak-Zhuang syndrome (EPAS1) a rarer genetic setting; surgery is central where feasible and prognosis depends on location and WHO grade (Experimental and Therapeutic Medicine 2020).

How it differs from its parent: it is the functioning tumour whose hormone inhibits rather than stimulates, so its syndrome is subtle and most cases are found by obstruction or incidentally; duodenal tumours are usually small, often psammomatous and syndromic, whereas pancreatic tumours are larger and more often metastatic.

How common: about 1 in 40 million (Experimental and Therapeutic Medicine 2020).

Treatment: resection (pancreatoduodenectomy or local excision by size and site); the parent page's pathways (somatostatin analogues, everolimus, sunitinib, peptide receptor radionuclide therapy) for metastatic disease, with grade guiding the choice; NF1 patients are screened for other tumours.