Oncocytic features are a hallmark of renal oncocytoma, but can be seen in other renal tumors such as clear cell renal cell carcinoma with granular cells and eosinophilic variant of chromophobe cell tumors. Up to 5% of renal neoplasms are ultimately diagnosed as unclassified renal cell carcinoma with oncocytic features accounting for a significant number of these tumors. Also a recent morphological variant of mucinous tubular and spindle cell carcinoma with oncocytic changes has been described, adding another challenge. Here we report an unusual case of unclassified renal cell carcinoma with extensive oncocytic changes and we discuss the differential diagnosis.
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