Primary multipotential malignant neoplasm of bone: chondrosarcoma associated with squamous cell carcinoma.

A primary neoplasm of the proximal humerus in a 68-year-old woman was unique histologically in that it contained both malignant cartilaginous and squamous cell components. The epithelial differentiation was confirmed by the demonstration of keratin by immunohistochemical techniques and of basement membrane, tonofilaments, and well-formed desmosomes by electron microscopy. The patient died 3 1/2 years after the onset of symptoms, without clinical evidence of either a primary tumor elsewhere or metastasis. The differential diagnosis from other bone tumors with epithelial differentiation, such as adamantinoma and "primitive multipotential primary sarcoma," is discussed. This is a rare primary neoplasm of bone of unknown histogenesis. Intermutability or metaplasia between mesenchymal and epithelial tissues is a possibility. The tumor probably originated from multipotential stem cells with the ability to undergo biphasic or dual differentiation toward mesenchymal and epithelial elements.