title: Flat intraepithelial lesions of the urinary bladder.
abstract: BACKGROUND
  In the 1998 World Health Organization and International Society of Urologic Pathology (WHO/ISUP) classification system for bladder neoplasms, flat intraepithelial lesions of the urinary bladder were categorized as reactive atypia, atypia of unknown significance, dysplasia, and carcinoma in situ. The clinical outcomes of patients diagnosed with these atypical urothelial proliferations are uncertain.
  
  
  METHODS
  The authors studied a series of patients who were diagnosed with reactive atypia of the urinary bladder (25 patients), urothelial atypia of unknown significance (35), or urothelial dysplasia (26) between 1985 and 1993. All histologic slides were reviewed and classified according to the 1998 World Health Organization and International Society of Urologic Pathology classification system. Patients with a concomitant or prior history of carcinoma in situ or urothelial carcinoma were excluded.
  
  
  RESULTS
  Patient age at diagnosis ranged from 24 to 88 years (mean, 65 years). The male-to-female ratio was 3:1. The mean follow-up was 3.9 years (range, 0.1-13.4 years; median, 3.5 years). None of the patients with reactive atypia or atypia of unknown significance developed dysplasia, carcinoma in situ, or urothelial carcinoma. Four patients (15%) with urothelial dysplasia developed biopsy-proven cancer, including 3 patients with muscle-invasive cancer. The mean interval from the diagnosis of urothelial dysplasia to the development of cancer was 4.5 years.
  
  
  CONCLUSIONS
  Patients with a diagnosis of urothelial atypia of unknown significance or reactive atypia do not have adverse clinical outcomes, whereas patients with urothelial dysplasia of the bladder have an increased risk for the development of carcinoma in situ and urothelial carcinoma.
authors.affiliation: Department of Pathology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
authors.forename: L
authors.initials: L
authors.lastname: Cheng
authors.forename: J C
authors.initials: JC
authors.lastname: Cheville
authors.forename: R M
authors.initials: RM
authors.lastname: Neumann
authors.forename: D G
authors.initials: DG
authors.lastname: Bostwick
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D002278:Carcinoma in Situ / Q000145:classification / Q000473:pathology; D002295:Carcinoma, Transitional Cell / Q000145:classification / Q000473:pathology; D002455:Cell Division; D002471:Cell Transformation, Neoplastic / Q000473:pathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D011230:Precancerous Conditions / Q000145:classification* / Q000473:pathology; D011379:Prognosis; D012307:Risk Factors; D012737:Sex Factors; D001749:Urinary Bladder Neoplasms / Q000145:classification* / Q000473:pathology; D019459:Urothelium / Q000473:pathology; D014944:World Health Organization