This classification is based primarily on the microscopic characteris tics of tumours and therefore is concerned with morphologically identifiable cell types and histological patterns as seen with conven tional light microscopy. The term tumour is used synonymously with neoplasm. The phrase tumour-like is applied to lesions that clinically or morpholog ically resemble neoplasms but do not behave biologically in a neo plastic manner. They are included in this publication because they give rise to problems in differential diagnosis and because of the un clear distinction between neoplasms and...

The 1973 WHO classification of bladder tumours anticipated a probable need for eventual revision of the criteria for diagnosing papillary and flat bladder neoplasia. A workshop sponsored by the WHO consisting of pathologists, urologists, cytologists, oncologists and basic scientists interested in bladder tumours addressed this subject, and after a follow- -up meeting sponsored by the International Society of Urological Pathology, the classification and terminology used in this text were agreed upon. A major change is in the introduction of a new category: papillary urothelial neoplasm of low...