Clear cell urothelial carcinoma of bladder: Case report of a rare and aggressive variant with review of literature.

Clear cell urothelial carcinoma is a rare variant of urothelial carcinoma. It's recognition and accurate diagnosis are essential in deciding appropriate treatment protocols considering the prognosis of this variant. A 57-year-old male presented with a history of hematuria and lower urinary tract symptoms for 6 months. Microscopically, the tumor was arranged in sheets and had a nested pattern. The tumor was composed of round to polygonal cells with abundant clear cytoplasm (>90% clear cell differentiation), resembling a conventional clear renal cell carcinoma. On special stain, the tumor was positive for periodic acid-Schiff (PAS) and negative for periodic acid-Schiff with diastase (PAS-D) and mucicarmine stain. The urothelial origin of clear cells was confirmed by positivity for GATA Binding protein 3(GATA3) and High Molecular Weight Cytokeratin (HMWCK) immunohistochemistry and negativity for NK3 homeobox 1(NKX3.1), Prostate specific antigen (PSA) and Paired box gene 8 (PAX8) immunohistochemistry.