EPITHELIOID OSTEOSARCOMA OF BONE - IMMUNOCYTOCHEMICAL EVIDENCE SUGGESTING DIVERGENT EPITHELIAL AND MESENCHYMAL DIFFERENTIATION IN A PRIMARYOSSEOUS NEOPLASM

Background. The combination of a primary osteosarcoma of bone with a s econd carcinomatous cell type has been recognized, although immunohist ochemical studies currently have not been performed in an attempt to u nderstand the histogenesis of such a tumor. Methods. In this report, t he authors performed immunohistochemical studies on a primary osseous carcinosarcoma. Using a biotin-streptavidin peroxidase conjugate techn ique, the expression of keratin, epithelial membrane antigen, and vime ntin was analyzed. Results. The epithelial cells expressed cytokeratin and epithelial membrane antigen but did not express vimentin. The mes enchymal cells strongly expressed vimentin, and only rare cells expres sed cytokeratin. Conclusions. The clinical, morphologic, and immunophe notypic data in this instance strongly suggest divergent differentiati on of a primitive multipotential uncommitted stem cell in a primary os seous tumor.