Answer: Clear cell adenocarcinoma

Histology: see below

Discussion: Clear cell adenocarcinoma of urothelial origin are rare aggressive tumors that can be encountered in the urinary bladder and urethra. They are to be distinguish from the more common benign lesions sharing some architectural and immunophenptypic features, namely: nephrogenic adenoma (NA). NA display tubulopapillary structures lined by single layer of bland cuboidal epithelial cells with low mitotic activity. Tubular structures in NA are frequently surrounded by distinct ring-like basement membrane and may contain eosinophilic to mucinous secretions and can be lined by hobnailed nuclei. Clear cell adenocarcinoma displays higher degree of nuclear atypia and mitotic activity compared to NA. The diagnosis of NA should be questioned in the presence of identifiable mitotic figure especially on limited biopsy. Both lesions are positive for PAX2 and PAX 8 and negative for HMWCK and p63. The higher rate of proliferative activity in clear cell Adenocarcinoma can be further illustrated by their high Ki67 index compared to NA. Intriguingly, the deeper portion of the current lesion had distinctly less cytologic atypia and lacked the high ki67 index raising the possibility of a coexisting NA component.