Sarcomatoid renal cell carcinoma with divergent sarcomatoid growth patterns: a case report and review of the literature.

A 71-year-old woman who presented with left abdominal pain was found to have a noncalcified renal mass with a perisplenic extension on imaging studies. Histologically, the tumor showed predominantly malignant spindle cells with extensive osteoid and chondroid matrix production. Various growth patterns resembling rhabdomyosarcoma, malignant fibrous histiocytoma, and fibrosarcoma were also observed. Immunohistochemistry showed positive staining of the neoplastic cells for cytokeratin and focally positive staining for CD10 and CD117 (c-Kit). Electron microscopic examination revealed a poorly differentiated neoplasm with both mesenchymal and epithelial features. The tumor was diagnosed as a sarcomatoid renal cell carcinoma with overgrowth of the sarcomatoid component (World Health Organization: renal cell carcinoma, unclassified). To our knowledge, sarcomatoid renal cell carcinoma with such a broad morphologic phenotype in a single case has not been documented. Furthermore, the CD117 expression in a sarcomatoid renal cell carcinoma that was observed in this case merits further investigation.