Insulinoma

Insulinoma
Pathology of pancreatic endocrine tumor (insulinoma).
Classification and external resources
Specialty	Oncology
ICD-10	C25.4, D13.7
ICD-9-CM	157.4, 211.7
ICD-O	M8151/1
DiseasesDB	6830
MedlinePlus	000387
eMedicine	med/2677
MeSH	D007340
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An insulinoma is a tumor of the pancreas that is derived from beta cells and secretes insulin. It is a rare form of a neuroendocrine tumor. Most insulinomas are benign in that they grow exclusively at their origin within the pancreas, but a minority metastasize. Insulinomas are one of the functional PanNET group ("functional" because it increases production of insulin; "PanNET" as an abbreviation of pancreatic neuroendocrine tumor). In the Medical Subject Headings classification, insulinoma is the only sub-type of "islet cell adenoma".

Beta cells secrete insulin in response to increases in blood glucose. The resulting increase in insulin acts to lower blood glucose back to normal levels at which point further secretion of insulin is stopped. In contrast, the secretion of insulin by insulinomas is not properly regulated by glucose and the tumors will continue to secrete insulin causing glucose levels to fall further than normal.

As a result, patients present symptoms of low blood glucose (hypoglycemia), which are improved by eating. The diagnosis of an insulinoma is usually made biochemically with low blood glucose, elevated insulin, proinsulin and C-peptide levels and confirmed by localizing the tumor with medical imaging or angiography. The definitive treatment is surgery.

Insulinomas are rare neuroendocrine tumours with an incidence estimated at 1 to 4 new cases per million persons per year. Insulinoma is one of the most common types of tumor arising from the islets of Langerhans cells (pancreatic endocrine tumors). Estimates of malignancy (metastases) range from 5% to 30%. Over 99% of insulinomas originate in the pancreas, with rare cases from ectopic pancreatic tissue. About 5% of cases are associated with tumours of the parathyroid glands and the pituitary (Multiple endocrine neoplasia type 1) and are more likely to be multiple and malignant. Most insulinomas are small, less than 2 cm.

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