[Small-cell variant of renal oncocytoma].

Renal oncocytoma is a distinct benign tumor accounting for approximately 3-5% of all renal tumors. This neoplasm is easily recognizable in its classic form: there are polygonal cells with abundant granular eosinophilic cytoplasm filled with mitochondria. The tumor cells are arranged in nests and tubular pattern. Here, 1 case of renal oncocytoma with a domination of small cells is reported (the so-called "oncoblasts") arising in elderly woman. These small cells have scant cytoplasm, dense hyperchromatic nuclei, and a high nuclear/cytoplasmic ratio. The term "small-cell variant of renal oncocytoma" was proposed for these cases. The unusual extensive small-cell component of the tumor may represent a potential diagnostic pitfall for primary or metastatic malignant small cell tumors.