The grading of bladder cancer is closely related to its recurrence and invasive behavior. The malignancy of bladder tumors is indicated by grading (Grade). Currently, the WHO grading system (WHO 1973, WHO/ISUP 1998, WHO 2004) is widely used for bladder cancer grading.

1. WHO 1973 Grading: The 1973 histological grading system for bladder cancer classifies cancer cells into three grades based on their differentiation: well-differentiated, moderately differentiated, and poorly differentiated, represented by grade 1, 2, 3 or grade I, II, III.

2. WHO/ISUP Grading: In 1998, the WHO and the International Society of Urological Pathology (ISUP) proposed a new classification for non-invasive urothelial (transitional cell) carcinoma, which was officially published by WHO in 2004. This grading system classifies urothelial tumors into papillary urothelial neoplasms of low malignant potential (PUNLMP), low-grade, and high-grade urothelial carcinoma.

The WHO 1973 and WHO 2004 grading systems are two different classification systems and cannot be directly compared.