Answer: Sarcomatoid renal cell carcinoma with chromophobe renal cell carcinoma component

Histology: This tumor is biphasic, with some areas consisting of a pleomorphic sarcomatoid growth pattern, in areas showing a prominent storiform pattern resembling malignant fibrous histiocytoma. Large areas of necrosis are present. Other areas of the tumor show classic histological features of a chromophobe renal cell carcinoma, consisting of nests of cells with lightly eosinophilic fine granular cytoplasm. These cells have distinct cytoplasmic borders, characteristic of chromophobe renal cell carcinomas. The nuclear features are also typical, consisting of irregular nuclei with a crinkly appearance, often containing a perinuclear halo. In areas, both the sarcomatoid and epithelial component are intimately admixed.

Discussion: These features are classic for sarcomatoid renal cell carcinoma. Although it has been described that chromophobe renal cell carcinomas are the most common renal epithelial tumor to be associated with a sarcomatoid growth pattern, in our experience this is relatively uncommon. More commonly we have seen clear cell renal cell carcinoma associated with sarcomatoid features. Although sarcomatoid renal cell carcinoma is described as a special variant of renal cell carcinoma, it is more accurate to refer to it as a pattern of poorly differentiated tumor that can be seen with any of the subtypes of renal cell carcinoma. The advantage of designating sarcomatoid renal cell carcinoma as a specific variant of renal cell carcinoma is that it has a distinctly poor prognosis regardless of the associated renal cell carcinoma pattern. Even relatively focal sarcomatoid features within an ordinary renal cell carcinoma is associated with a poor prognosis. By definition, all sarcomatoid renal cell carcinomas are Fuhrman nuclear grade IV.