Clusters of epithelioid cells are separated by mature adipose tissue. The presence of cytoplasmic clearing results in close resemblance to clear cell renal cell carcinoma. However, the tumor does not have the vascular pattern seen in renal cell carcinoma. The presence of adipocytes and dysmorphic blood vessels were additional help clues. In difficult cases, immunostains can be done. Renal cell carcinomas are usually positive for EMA/MUC1, CD10, CA9 and cytokeratins and negative for melanocytic markers such as HMB-45 and Melan-A. Angiomyolipomas would be positive for melanocytic markers and smooth muscle actin and negative for cytokeratins, CD10, and EMA.
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