Histologic variants of urothelial bladder cancer and nonurothelial histology in bladder cancer.

Bladder cancer can be classified histologically as urothelial or non-urothelial. Urothelial cancer has a propensity for divergent differentiation, which has increasingly been recognized in recent years due to heightened awareness and improved immunohistochemistry techniques. Furthermore, the recent World Health Organization classification of urothelial cancers improved clarity on this issue, with its listing of 13 histologic variants of urothelial cancer. The divergent differentiation patterns include, amongst others, squamous, glandular, micropapillary, nested, lymphepithelioma-like, plasmacytoid and sarcomatoid variants of urothelial cancer. Attempts to quantify the amount of divergent differentiation present, such as using the nonconventional differentiation number, have been made recently, which will improve the ability to compare publications from different centres. Genetic-based studies have indicated that the histologic variants of urothelial cancer arise from a common clonal precursor. Mostly, the current evidence suggests that urothelial cancer with divergent differentiation has a worse prognosis when compared with pure urothelial cancer. This article will review the current literature on variant histologies of urothelial cancer, and well as new developments in pure squamous cell carcinoma, small cell carcinoma and adenocarcinoma of the bladder.