The 2004 WHO classification of bladder tumors: a summary and commentary.

The key points of the latest World Health Organization (WHO) classification of non-invasive urothelial tumors are the following: the description of the categories has been expanded to improve their recognition; a tumor with particularly good prognosis (papillary urothelial neoplasm of low malignant potential) no longer carries the label of 'cancer'; it avoids the use of ambiguous grading such as grade 1/2 or 2/3 (as done in the 1973 WHO classification); the group of noninvasive high-grade carcinoma is large enough to virtually contain all those tumors having biological properties similar to those seen in invasive urothelial carcinoma, and a similarly high level of genetic instability. This scheme is meant to replace the 1973 WHO classification, but the use of both the 1973 and the latest WHO classifications is recommended until the latter is sufficiently validated.