Microcystic transitional cell carcinoma: a report of 2 cases arising in the renal pelvis.

Microcystic transitional cell carcinoma is a rare variant of urothelial carcinoma; to date, it has been described only in the urinary bladder. We report 2 cases of microcystic transitional cell carcinoma arising in the renal pelvis. The first case occurred in a 73-year-old man with a history of superficially invasive transitional cell carcinoma who presented with macroscopic hematuria and anemia. The second case occurred in a 62-year-old woman who had no relevant medical history and presented with hematuria. Computed tomographic scan revealed a tumor of the renal pelvis. In both cases, microscopic examination showed invasive transitional cell carcinoma with prominent cystic features. The cysts were irregular in size and were deeply infiltrative. The cysts were lined by single or multiple layers of cuboidal or flattened cells with minimal cytological atypia. The first patient died of his disease 18 months after presentation. The second patient remained well at her 6-month follow-up examination. Microcystic transitional cell carcinoma is an unusual, deceptively bland variant of urothelial carcinoma, which can mimic benign lesions.