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Malignant fibrous histiocytoma (giant cell type) of the pancreas. A distinctive variant of osteoclast‐type giant cell tumor of the pancreas

Malignant giant cell tumors of the pancreas are rare neoplasms which have been generally thought to represent epithelial malignancies of either acinar or ductal epithelium. The authors have studied a tumor of the pancreas that was characterized histologically by a proliferation of benign‐appearing osteoclast‐type giant cells in association with atypical, often bizarre mononuclear cells. Immunohistochemical studies demonstrated negative staining of the tumor cells with epithelial markers, including low‐molecular weight keratins, carcinoembryonic antigen and epithelial membrane antigen, and positive staining with vimentin antibodies, supporting a fibroblastic line of differentiation. Electron microscopic examination also showed absence of ultrastructural features of epithelial differentiation such as microvilli, intercellular junctions, or desmosomes. The authors believe the current case represents a true sarcoma of the pancreas, currently best classified as a malignant fibrous histiocytoma, giant cell type. This tumor should be distinguished from the epithelial type of osteoclastic giant cell tumor of the pancreas.