[New WHO classification of urothelial carcinoma of the urinary bladder]

The WHO classification of urothelial carcinomas of the urinary bladder (1999) presents the papillary urothelial neoplasia of low malignant potential (PUNLMP) as a new entity in between the papillomas and the papillary urothelial carcinomas. This neoplasia shows a typical basal palisading, a low mitotic rate, and a low MIB-1-proliferation index. The PUNLMP is said to have an increased risk of development of recurrent papillary lesions with the possibility of malignant transformation. At present, there is an intensive discussion on this new entity. The participants of a meeting on the consensus classification on urothelial tumors held in Ancona in 2000 have meanwhile split in two discussion groups. One favors the new WHO classification with the papillary urothelial carcinomas G I, G II, and G III, but without PUNLMP, whereas the other group favors the consensus classification of 1998 with papillomas, papillary urothelial neoplasia of low malignant potential, and non invasive as well as invasive low-grade and high grade papillary urothelial carcinomas. Future long term prospective studies will show the significance of PUNLMP compared to well differentiated non invasive papillary urothelial urinary bladder carcinoma G I (G Ia). Otherwise, there is no significant difference in the classification of carcinomas and non epithelial lesions compared with the previous classification of 1973. The new WHO does however discriminate the minimally invasive papillary urothelial carcinomas in those with infiltration of the lamina propria above the muscularis mucosae (pT1a), the infiltration of the lamina muscularis mucosae (pT1b), and the extension beyond the muscularis mucosae (pT1c). The recurrence rate increases from stage pT1b. This substaging may be of therapeutical relevance.