Cystic neoplasms of the pancreas are rare and often mistaken for pseudocyst by imaging studies and macroscopic examination. We describe an unusual tumor of the pancreas composed of a mural nodule of anaplastic carcinoma arising from a huge ductal adenocarcinoma undergoing cystic degeneration. The cyst measured 27 × 13 × 4 cm. Light microscopy showed that the cyst was partly lined by a single layer of cuboidal to columnar tumor cells with focal mucin production and was surrounded by hyalinized connective tissue. Most lining epithelial cells were absent owing to extensive degenerative process. Immunohistochemical studies showed positive staining of cytokeratin and vimentin for pleomorphic giant tumor cells, which were negative for leukocyte common antigen (CD45), KP-1 (CD68), epithelial membrane antigen (EMA), and carcinoembryonic antigen (CEA). The ductal adenocarcinoma stained strongly positive for cytokeratin and EMA, and negative for vimentin, CD45, CD68, and CEA. The clinical course of the current case was extremely poor and the prognosis resembled that of an anaplastic carcinoma. Therefore, we like to emphasize the importance of complete excision and extensive sampling of any cystic neoplasms in the pancreas including those with large cystic component to avoid missing the malignant elements.
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