Variants of urothelial carcinoma apart from those with glandular, squamous or neuroendocrine differentiation: key morphologic features, differential diagnoses and prognostic significance

Urothelial carcinoma of the bladder may exhibit divergent differentiation and can present a challenge to the reporting pathologist. A variety of different morphologic subtypes have been described, many of which are included in the 2004 World Health Organization Classification. Some of these may impact on prognosis and direct therapy accordingly. This article presents an overview of the variant histological types of urothelial carcinoma of the bladder, apart from glandular, squamous and neuroendocrine differentiation, with an emphasis on key morphological features and potential differential diagnoses.