PATHOLOGY

Benign urothelial papilloma of the bladder: a review of 34 de novo cases
Magi-Galluzzi C, Epstein JI
The Cleveland Clinic Foundation, Cleveland, OH, and The Johns Hopkins Hospital, Baltimore, MD, USA
Mod Pathol. 2004; 17 (suppl 1): 165A

• Background: Urothelial papilloma of the bladder is an uncommon entity that represents less than 3% of papillary urothelial neoplasms, when using restrictive diagnostic criteria. The biologic potential of urothelial papilloma of the bladder is uncertain as there are only limited studies published on this issue.
• Design: We retrospectively studied 34 patients who were diagnosed with urothelial papilloma of the bladder at one of our institutions between 1989 and 2002. 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. All histologic slides were reviewed and met the diagnostic criteria of the 1998 WHO / ISUP classification system.
• Results: The mean age of the patients at diagnosis was 57.8 (range, 23-87 years). The male-to-female ratio was 2.4:1 (24 males and 10 females). The tumor size ranged from one 2X to one 40X microscopic field. Some of the distinctive histological features seen were changes in the umbrella cells: vacuolization (4); prominence with cytological atypia (2); eosinophilic cuboidal morphology (1); hobnail morphology (1); and mucinous metaplasia (1). Also noted in 3 cases was prominent edema of the fibrovascular stalks mimicking polypoid cystitis. 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; one 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 for unrelated causes. None of the patients died of bladder cancer.
• Conclusions: 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.
  
  
• Editorial Comment
  In the World Health Organization / International Society of Urological Pathology (WHO / ISUP) consensus classification of urothelial (transitional cell) neoplasms of the urinary bladder (Am J Surg Pathol. 1998; 22:1435-48), papilloma is a distinct neoplasm from papillary neoplasm of low malignant potential. The former neoplasm is defined as discrete papillary growth with central fibrovascular core lined by urothelium of normal thickness and cytology, frequent vacuolization of umbrella cells and edema of the stroma. There is no need to count the number of cell layers. It is a rare benign condition comprising less than 3% of papillary urothelial neoplasms. Papillary urothelial neoplasm of low malignant potential is a papillary lesion with minimal architectural abnormalities and minimal nuclear atypia irrespective of cell thickness. In general, the major distinction from papilloma is that in papillary urothelial neoplasm of low malignant potential the urothelium is much thicker and/or nuclei are significantly enlarged. The urothelial papilloma, in contrast, has no architectural or cytological atypia.
  Both papilloma and papillary urothelial neoplasm of low malignant potential may develop recurrent or new papillary lesions but only the latter may be associated with invasion or metastases in rare cases. The study by Magi-Galluzzi and Epstein disclosed the clinical behavior of 34 de novo papillomas. The follow-up showed that 6 patients had recurrent disease but none progression to either lamina propria (T1) or muscularis propria (T2) invasion. This paper confirms that papilloma and papillary neoplasm of low malignant potential should be considered separately. The urologist should follow-up patients with papilloma but because they have a low incidence of recurrence and rarely progress to develop noninvasive urothelial carcinoma, it seems reasonable to avoid labeling these patients as having cancer.

Dr. Athanase Billis
Full-Professor of Pathology
State University of Campinas, Unicamp
Campinas, São Paulo, Brazil