The WHO/ISUP 1998 and WHO 1999 systems for malignancy grading of bladder cancer. Scientific foundation and translation to one another and previous systems

Recently, two new classification systems for grading of urothelial neoplasms have been published. The objective of both was to avoid the overdiagnosis of cancer and to create better criteria for the grades. The WHO/ISUP classification of 1998 distinguishes papilloma, papillary urothelial neoplasm of low malignant potential (PUNLMP), low and high grade carcinomas, whereas the WHO 1999 system subdivides the high grade into grades 11 and 111, and is otherwise identical. This note summarizes studies supporting the rationale of the two new systems, describes pattern recognition criteria for the grades, and highlights the homology between them.