ISLET CELL TUMORS OF THE PANCREAS

Abstract

Neuroendocrine tumors of the pancreas are neoplasms arising predominantly from the pancreatic Islets of Langerhans and are thus known as islet cell tumors. Islet cell tumors are rare, with an overall incidence of 1 to 1.5 per 100,000 in the general population.¹⁶ Neuroendocrine tumors are characterized histologically by the presence of neurosecretory granules. Under light microscopy, these tumors exhibit a bland, monotonous appearance with relatively uniform, well-differentiated cells with homogenous small nuclei, few if any nucleoli, abundant cytoplasm, and a low mitotic rate.

Neuroendocrine tumors are carcinomas and therefore stain positively for cytokeratins. The presence of neurosecretory granules is demonstrated by positive chromogranin, synaptophysin, or Gremilius stains. Neuron-specific enolase is less specific and should not, by itself, be accepted as diagnostic of a neuroendocrine tumor. Immunohistochemical staining for specific hormones that these tumors secrete may allow for further tumor characterization or may confirm a clinical suspicion.

Up to half of all islet cell tumors secrete one or more biologically active peptides that result in systemic clinical symptoms. These tumors are called functional islet cell tumors, and it is the resulting clinical syndromes that bring patients with these tumors to medical attention. Because of the nonspecific and intermittent nature of their symptoms, however, diagnosis is commonly delayed by months to years.15, 26The time from development until diagnosis for nonfunctioning islet tumors may be even longer because these patients have no associated systemic symptoms. Rather, they are diagnosed either on the basis of symptoms caused by tumor bulk or on the basis of incidental findings during unrelated medical evaluations.