Mucinous cystadenocarcinoma of the pancreas. Morphologic and immunocytochemical observations.

Twenty mucinous cystadenocarcinomas of the pancreas, most of which occurred in the tail of the pancreas in middle-aged women, were examined histologically and by immunohistochemical stains. Thirteen tumors displayed a marked histological heterogeneity and expressed intestinal differentiation as shown by the colonic appearance of the glands both at the light- and electron-microscopic levels. Other intestinal features included varying numbers of goblet cells, argyrophil and argentaffin cells, and even Paneth cells. By immunohistochemistry, endocrine cells were present in 13 of the 20 tumors (65%) and were more numerous in the poorly differentiated than in the well-differentiated epithelial component of the tumors. Serotonin-containing cells were the most common endocrine cells, followed by somatostatin-containing cells and cells that showed immunoreactivity for pancreatic polypeptide and gastrin. However, none of the patients had clinical manifestations of carcinoid, somatostatinoma, or the Zollinger-Ellison syndrome. The findings support the hypothesis that mucinous cystadenocarcinomas of the pancreas arise from an "endodermal stem cell" that differentiates into cells with intestinal phenotypes.