Variants of Bladder Cancer: The Pathologist's Point of View

Pathologic evaluation of bladder cancer typically reveals great tumor heterogeneity and, therefore, the common observation of urothelial carcinoma exhibiting a wide variety of histopathologic patterns is not surprising. Some of these patterns are so distinctive that they have been recognized as specific variants of urothelial carcinoma. Classifications have recently been revised in the 2016 World Health Organization Classification of Tumors of the Urinary System and Male Genital Organs. The current World Health Organization classifications clarify terminological issues and provide better definition criteria, but also incorporates some new entities. Many of these variants have important prognostic or therapeutic implications worth knowing by the urologist and oncologist, but also represent diagnostic challenges in daily practice of pathology. This review will discuss the features of pathologic variants of bladder cancer in the context of our current clinical practice.