Urothelial carcinoma constitutes most of the bladder cancers. However, urothelium lining the bladder has the capacity of differentiation towards many different cells and likewise carcinomas arising from urothelium produce quite different morphological variants. There are several carcinoma variants including those commonly seen in other organs like micropapillary carcinoma as well as those resembling benign lesions more specifically found in bladder such as nested variant. Recent WHO classification in 2004 specified a number of different variants having diverse clinical and morphological features and additional variants have also been identified in recent years. In this paper, the differentiation capacity of urothelium, characteristics of new variants, morphological and definitional problems, as well as suggestions for future classifications are discussed.

Keywords: Urothelial carcinoma, variants, urothelium, urinary bladder