Insulomas - The value of precise morphologic diagnosis

Sixteen cases of pancreatic islet cell tumors were investigated to determine the exact cell types involved. Additional histochemistry and electron microscopy made it possible to establish a precise cytological diagnosis in thirteen instances. Electron microscopy allows an easy distinction between beta and alpha cells but is less accurate for differentiation of alpha-1 and alpha-2 cells. The usual cytological criteria for the distinction of malignant from benign tumors do not necessarily apply in pancreatic islet cell tumors, the existence of metastases being the only reliable sign of malignancy. In the absence of metastases the interpretation should be limited to the terms "benign" or "malignancy suspected", according to the histological appearance. Common aspects of pancreatic islet cell tumors and carcinoid tumors suggest that their cells have an origin analogous to that of the endocrine cells of the gastrointestinal tract or that both groups belong to the larger group of so-called APUD cells. © 1973 Springer-Verlag.