Sarcomatoid renal carcinoma: the final common dedifferentiation pathway of renal epithelial malignancies.

Sarcomatoid renal carcinoma (SRC) is an aggressive neoplasm with an age and gender distribution similar to that of conventional (clear cell) renal cell carcinoma (RCC). Genetic and morphologic evidence indicates that the tumor results from de-differentiation of renal epithelial malignancy and associations with RCC, papillary renal carcinoma, chromophobe renal carcinoma and collecting duct carcinoma have been reported. The tumor is composed of sheets of malignant spindle cells that have immunohistochemical and ultrastructural features of both stromal and epithelial cells, and may contain myxoid areas containing osteoclast-like giant cells or pleomorphic sarcomatoid spindle cells resembling rhabdomyoblasts. Rare cases of osteogenic SRC have been described. The tumor shows marked proliferative activity in growth kinetic studies and is usually associated with a poor patient survival that is best predicted by staging.