Osteogenic and sarcomatoid differentiation of a renal cell carcinoma

Sarcomatoid renal cell carcinoma is an uncommon renal tumor, and osteogenic differentiation has been reported in only a few of these tumors. The authors report such a case with radiographic, light microscopic, and electron microscopic findings, which demonstrate that the sarcomatoid areas of the tumor are derived from the malignant epithelial cells, retaining epithelial features such as desmosomes and lumina with microvilli. The use of electron microscopy is important in the establishment of this diagnosis.