Comparison of 1998 WHO/ISUP and 1973 WHO classifications for interobserver variability in grading of papillary urothelial neoplasms of the bladder. Pathological evaluation of 258 cases.

Aim: Our aim was to compare the interobserver variability between the 1998 WHO/ISUP and 1973 WHO classifications.

Methods: 258 consecutive papillary urothelial carcinomas were reviewed by two pathologists and assigned a tumor grade according to the 1973 WHO and 1998 WHO/ISUP without the knowledge of primary diagnosis and clinical follow-up. All cases were also histologically staged by the two pathologists separately as follows: pTa (noninvasive), pT1 (lamina propria invasion only), pT2 (muscularis propria invasion). Findings of both pathologists and degree of agreement were compared statistically by using Pearson's chi(2) test and kappa statistics respectively. A kappa value of 0.21-0.40 is accepted as fair, 0.41-0.60 moderate and 0.61-0.80 substantial agreement.

Results: Regardless of the pathologist, tumor grades of two classifications correlated to each other and the pathological stage (p < 0.05). Overall degree of agreement between pathologists was higher in the 1998 WHO/ISUP (kappa 0.59) than the 1973 WHO (kappa 0.41), but both were still moderate. Papillary urothelial neoplasia with low malignant potential was the group of 1998 WHO/ISUP that showed the lowest degree of agreement and if excluded, interobserver variability of the 1998 WHO/ISUP decreased significantly (kappa 0.84).

Conclusion: The diagnosis of papillary urothelial neoplasia with low malignant potential and the criteria that differentiates it from low-grade carcinomas needs improvement in order to compare the different studies and therapies and to provide more accurate information for management.