Urothelial papilloma of the bladder: a review of 34 de novo cases.

Background: Urothelial papilloma of the bladder is an uncommon entity when using restrictive diagnostic criteria.
Design: We retrospectively studied 34 patients who were diagnosed with urothelial papilloma of the bladder using the criteria of the 1998 WHO/ISUP classification system. Six cases were in-house and the remaining 28 were referred from other institutions as consults to one of the authors. In all cases, the diagnosis of papilloma was the first manifestation of urothelial neoplasia.
Results: The mean age of the patients at diagnosis was 57.8 years (range, 23-87 years). The male-to-female ratio was 2.4:1 (24 males and 10 females). The tumor size averaged 3.3 mm (range, 1-20 mm; median, 2 mm). Simple papillary fronds were seen in all cases; in 5 cases the additional finding of secondary budding off of small fronds from larger ones was also seen. In all cases, the fronds had a round morphology; yet in 4 cases elongated fronds were also noted. In 5 cases, dilated lymphatics within the fibrovascular fronds were apparent. One case had foamy histiocytes within the fibrovascular stalks. In all cases, the lining consisted of normal-appearing urothelium without hyperplasia, dysplasia, and/or mitotic figures. Some of the distinctive histologic features seen were changes in the umbrella cells: vacuolization (n = 4), prominence with cytologic atypia (n = 2), eosinophilic syncytial morphology (n = 1), apocrine-like morphology (n = 1), and mucinous metaplasia (n = 1). Follow-up was available in 26 cases with a mean follow-up for those without evidence of progression of 28.9 months (range, 3-127 months). Three patients (8.8%) developed recurrent papilloma 4, 15, and 18 months after the initial diagnosis of papilloma; 1 of these patients also showed progression to noninvasive low-grade urothelial carcinoma at the time of recurrence (15 months). Three patients (8.8%) progressed to higher-grade disease: 2 to noninvasive low grade urothelial carcinoma (11 and 15 months after the original diagnosis) and 1 to a papillary urothelial neoplasm of low malignant potential at 104 months and a noninvasive low-grade urothelial carcinoma at 141 months from the initial diagnosis of papilloma. None of the patients demonstrated progression to either lamina propria (T1) or muscularis propria (T2) invasion. Two patients died of unrelated causes. None of the patients died of bladder cancer.
Conclusion: Patients with urothelial papillomas have a low incidence of recurrence and rarely progress to develop urothelial carcinoma. It seems reasonable to avoid labeling these patients as having cancer. It remains to be studied whether and when patients with papillomas who have no evidence of recurrence or progression no longer need to be followed.