Pleomorphic carcinoma of the pancreas with osteoclast-like giant cells.

We studied two cases of pleomorphic carcinoma of the pancreas with osteoclast-like giant cells. The cut surface of both tumors was firm and whitish-tan in color, with extensive hemorrhage and necrosis. Microscopically, these tumors were composed mainly of pleomorphic mononuclear cells and numerous bizarre giant cells, with a spindle-cell sarcomatoid appearance and adenocarcinomatous elements exhibiting varying degrees of differentiation. Multinucleated giant cells resembling osteoclasts were frequently located around sites of necrotic hemorrhage. Immunohistochemically, most tumor cells of sarcomatous areas and some anaplastic giant cells were positive for vimentin and cytokeratin. Both carcinoembryonic antigen and CA 19-9 were detected in tumor cells in one case, forming ducts or glands. These findings suggest that the tumors in these two cases originated from pancreatic-duct cells with mesenchymal differentiation. In contrast, osteoclast-like giant cells in both cases showed strong immunoreactivity with vimentin and with KP1 and PG-M1 (CD68), which are monoclonal antibodies that react with a histiocyte-macrophage-associated antigen; however, there was no reaction with any epithelial markers. Thus, osteoclast-like giant cells are not epithelial in nature, suggesting that their origin of histiocyte-macrophage lineage is possibly induced as a paraneoplastic product.