A 66-year-old woman was presented with the perirenal tumor 15 × 10 mm close to the superior pole of the right kidney. Macroscopically a perirenal tumor consisted of considerably fragile tissue fragment measuring 1.5 × 1.0 × 0.6 cm. Histologically, in routine hematoxylin-eosin stained sections the perirenal tumor was composed of polygonal clear cells or cells with eosinophillic cytoplasm with moderate epithelioid appearance (Fig. 1). In the most cells nuclear polymorphism was prominent. Up to 2-3 mitoses per 10 high-power fields were present. Furthermore, the tumor showed abundant vascularity (Fig. 2). The resection was microscopically incomplete.
Immunohistochemically cytokeratin AE1/AE3, cytokeratin 20, cytokeratin 7, CD10 and protein S-100 were negative, whereas we noted positivity of HMB-45 (++) (Fig. 3), alpha smooth actin (+++), vimentin (++), estrogen receptor alpha (++) and focally desmin (+). Nuclear immunoexpression of Ki67 was present in 8% of tumor cells. The small vessels were revealed using CD34 antibody.