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Osteogenic sarcoma with epithelial differentiation.

This case report details an osteogenic sarcoma arising in a vertebra in which cytokeratin intermediate filaments were detected immunohistochemically with three different antibodies. This feature was present not only in the primary neoplasm but also in two local recurrences and a metastasis to the iliac bone. What is unique about this primary bone tumor, however, is the structural evidence for epithelial differentiation. Ultrastructurally, well-formed desmosomes and tonofilaments were present in all four surgically resected specimens. This tumor expands the list of soft tissue and bone tumors in which anomalous expression of intermediate filaments can occur but, more important, illustrates that changes in genetic expression of neoplasia of mesenchymal origin can result in paradoxic epithelial differentiation.