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Cystadenoma with mesenchymal stroma is a rare neoplasm of the liver that occurs exclusively in young women and has a potential for malignant transformation. A light microscopic and immunohistochemical study of a case of biliary cystadenoma and another of biliary cystadenocarcinoma revealed a range of differentiation of the lining epithelial cells. The lining cells in the cystadenoma resembled the cells of the normal intrahepatic bile ducts. In contrast, the epithelial lining in the case of cystadenocarcinoma had features of intestinal mucosa, including goblet, Paneth, and endocrine cells similar to those found in other mucinous cystic neoplasms of the foregut area. The compact "ovarianlike" mesenchymal stromal cells had immunohistochemical characteristics of myofibroblasts. These are reactive contractile cells that may proliferate in response to the expanding cysts and female hormones, and they differ immunohistochemically from ovarian stromal cells.

True cystic neoplasms of the pancreas generally have mucinous, glycogen-rich, or acinar-type-cyst-lining epithelium. A malignant polycystic pancreatic neoplasm in a 74-year-old black woman whose cyst-lining epithelium had none of the above-cited attributes and thus appears to represent an exception is described. The primary tumor was a large, encapsulated mass whose cysts contained watery fluid. Basically, two types of epithelium lined the cysts: a single layered, low-grade malignant-appearing type and a proliferative, overtly malignant-appearing pseudostratified and papillary type. Oncocytic metaplasia, canaliculi, and microvilli were ultrastructural features.

A 74-year-old woman with a right ovarian tumor had a high level of the serum tumor marker alpha-fetoprotein (AFP). After combination chemotherapy, the serum AFP level decreased significantly. Histopathologic study of surgically excised tumor tissue revealed a serous papillary cystadenocarcinoma. By the indirect immunoperoxidase technique, the AFP was stained in the cytoplasm of the differentiated tumor cells, showing papillary or tubular structures. Serial sections showed that the cells containing PAS-positive substances did not correspond to those producing AFP.