Primitive multipotential primary sarcoma of bone: a case report and immunohistochemical study.

A tumor initially presenting as a round cell sarcoma in the proximal tibia of a 42-yr-old male disseminated to involve the femur, multiple tarsal bones, and the lungs. In addition to round cell areas resembling lymphoma, other areas of the tumor produced osteoid matrix and still other areas suggested epithelial differentiation. Immunohistochemical staining revealed the presence of epithelial markers in areas of epithelial differentiation, leukocyte markers in areas of lymphomatous differentiation, and neither marker in areas of osteosarcomatous differentiation. The finding of epithelial elements in a primary bone tumor is rare, and this report is one of the first confirming their presence using immunohistochemical markers. The findings are consonant for neither epithelial nor lymphoid neoplasms and in all probability represent multipotential differentiation in a primitive mesenchymal tumor.