Malignant pancreatic oncocytoma. An unusual cause of organic hypoglycemia

A case of malignant islet-cell tumor with oncocytic features occurring in a 54-year-old woman with symptoms of organic hypoglycemia is reported. The tumor was composed of ribbons of cells arranged in an endocrine pattern. The cytoplasm of these cells was eosinophilic and finely granular. Ultrastructurally, the cells contained numerous mitochondria and dense-core neurosecretory granules. Tumor cells were focally immunoreactive for neuron-specific enolase, insulin, glucagon and VIP. Capillaries invasion and metastases to lymph nodes argued in favor of malignancy but there was no subsequent malignant involvement during a 3-year follow-up after surgery. Such insulinomas with oncocytic features have not been previously described. Endocrine features in oncocytomas of the pancreas and of other locations are discussed.