Variant Histology in Bladder Cancer-Current Understanding of Pathologic Subtypes

Urothelial carcinomas (UC) are characterized by variant morphologies. However, the diagnosis of these variants can be challenging, in part due to their evolving diagnostic criteria. This review discusses the diagnostic criteria, molecular features, and prognostic implications of the UC variants. Evolving subtypes of UC are also briefly discussed.

The WHO 2016 classification of tumors of the urinary system has refined the morphologic criteria for the diagnosis of UC variants. Many of these follow a more aggressive clinical course, but conclusive data on their effect on survival are lacking. The molecular alterations characteristic of some of these variants may be amenable to targeted therapies. Accurate identification of variant histology in UC has important implications for patient management. Despite identification of distinct molecular alterations in some of these variants, current molecular classifiers of invasive UC have not been significantly analyzed in these subtypes, opening up areas of future research.