Duct-islet cell tumor of the pancreas. A case report with immunohistochemical and electron microscopic findings.

A case of pancreatic tumor with features of both duct and islet cell components was found incidentally at autopsy in a 76-year-old male who had died of intrahepatic cholangiocarcinoma. The tumor, measuring about 1.0 cm in diameter, was located in the pancreatic tail. The tumor was composed of two distinct cell populations, islet cells and duct cells. Immunocytochemically, nearly all of the former cells were positive for insulin but negative for cytokeratin, carcinoembryonic antigen (CEA) and mucin, while the latter were positive for cytokeratin, CEA and mucin but negative for insulin. Additionally, a majority of the tumor cells that had formed islet-like structures were positive for neuron-specific enolase (NSE), whereas NSE-positive cells were found only rarely in duct components. Electron microscopy confirmed the presence of two cell populations. Simultaneous occurrence of duct and islet cell components in a single pancreatic tumor indicates an intimate histogenetic relationship between pancreatic endocrine and duct cells.