The many faces of urothelial carcinoma: an update with an emphasis on recently described variants

Urothelial carcinoma is well known for its divergent differentiation. Several "variant" morphologies have been described in the literature in recent years and have additionally been recognized in the recent World Health Organization classification of urothelial neoplasms. The importance of recognizing these variant histologies lies in the potential diagnostic, prognostic, or therapeutic implications that accompany these diagnoses. The range of variant morphology seen in the urinary bladder may also be seen in urothelial tumors of the renal pelvis. Herein we review select variants of urothelial carcinoma focusing on the relatively recently recognized variants, outlining the diagnostic features, common differential diagnostic dilemmas, and clinical relevance. This review also includes a discussion on variants on which there is recent information available.