Non-papillary urothelial lesions of the urinary bladder: Morphological classification and immunohistochemical markers

In the past quarter century, several nomenclature systems for non-papillary urothelial lesions of the urinary bladder have been proposed. The 1998 World Health Organization and International Society of Urological Pathology (WHO/ISUP) classification recommended a four-tier system for the subdivision of flat intraepithelial lesions of the bladder. This classification was adopted by the WHO in 1999 and revised in 2004. In 2002, a more detailed classification of flat urothelial lesions was based on the Ancona International Consultation. Each of these lesions was defined with strict morphological criteria to provide more accurate information to urologists in managing patients. However, immunohistochemical markers including proliferation markers, cytoskeletal proteins, growth factors and their related receptors, cell adhesion molecules and oncogene proteins are increasingly being used in order to differentiate histologically similar lesions.