Objectives. To investigate the relation of the World Health Organization/International Society of Urological Pathology (WHO/ISUP) system for bladder neoplasia to prognosis. Methods. A total of 134 patients with pTa bladder tumors were identified. We excluded cases with prior or concurrent carcinoma in situ or invasion (pT1 or pT2). Progression was defined as a tumor recurrence with either lamina propria (pT1) or muscularis propria (pT2) invasion or carcinoma in situ. Age at diagnosis, sex, tumor size, multifocality, and grade (WHO, WHO/ISUP) were entered into a Cox multivariate analysis to predict progression. Results. The distribution of WHO papilloma, WHO G1, WHO G2, and WHO G3 was 5.2%, 31.3%, 59%, and 4.5%, respectively. The distribution of WHO/ISUP papilloma, tumors of low malignant potential, low-grade carcinomas, and high-grade carcinomas was 2.2%, 21.6%, 13%, and 21.6%, respectively. The mean and median follow-up was 56.2 and 50 months, respectively. The 90-month actuarial risk of progression for WHO papilloma, G1, G2, and G3 was 0%, 11%, 24%, and 60%, respectively. The corresponding progression rate for WHO/ISUP papilloma, tumors of low malignant potential, low-grade carcinoma, and high-grade carcinoma was 0%, 8%, 13%, and 51%, respectively. In separate analyses, WHO grade (P = 0.003) and tumor size (P = 0.03), as well as WHO/ISUP (P = 0.002) and tumor size (P = 0.04), independently predicted progression. Conclusions. WHO G3 has a more rapid progression rate and a slightly worse long-term progression rate compared with WHO/ISUP high-grade carcinoma. However, although only 4.5% of tumors were WHO G3, we were able to classify 21.6% as WHO/ISUP high-grade carcinoma with a poor prognosis. Use of the WHO/ISUP system allows urologists to more closely follow a larger group of patients at high risk of progression.
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