Objective: There are limited data on the distribution of bladder cancers in the general population, classified by World Health Organization (WHO)/International Society of Urological Pathology (ISUP) criteria. This study evaluated the classification and stage of bladder cancers as part of a population-based epidemiological study of bladder cancer in the Northeastern United States.
Material and methods: All New Hampshire residents with bladder cancer newly diagnosed from 1998 to 2000 were identified through the state cancer registry. All slides were reviewed by a single pathologist. Tumors were classified by two sets of standard criteria.
Results: The retrieval rate for cases was over 90%. Of 342 cases reviewed, 15 were excluded for technical reasons or because malignancy was not definitively diagnosed. According to WHO/ISUP criteria, 25.7% of tumors were papillary urothelial neoplasms of low malignant potential (PUNLMP), 34.3% low-grade papillary carcinomas, 22.6% high-grade papillary carcinomas, 10.1% non-papillary urothelial carcinomas and 5.5% carcinoma in situ. By WHO (1973) criteria, 52.5% of tumors were grade 1, 21.4% grade 2 and 26.1% grade 3. Two-thirds of all tumors were stage Ta, 20.8% stage T1 and 7.6% stage >or=T2. 100% of PUNLMPs were non-invasive, 6.3% of low-grade carcinomas were invasive and 64.9% of high-grade carcinomas were invasive.
Conclusions: Compared to clinic or hospital referral-based series, this study documents a higher percentage of non-invasive tumors and a lower percentage of muscle-invasive tumors. There was also a higher percentage of PUNLMP tumors and fewer high-grade papillary carcinomas than in other series. These results may more accurately reflect prevalence data for bladder cancer grade and stage, although geographic variability may exist.