title: Dual-track pathway of bladder carcinogenesis: practical implications.
abstract: BACKGROUND
  The concept of a dual-track pathway in bladder carcinogenesis postulates that bladder cancer develops via 2 distinct but somewhat overlapping pathways, termed the papillary and nonpapillary. Approximately 80% of bladder carcinomas consist of superficial exophytic papillary lesions that originate from urothelial hyperplasia. These typically low-grade papillary tumors may recur, but they rarely invade the bladder wall or metastasize. The remaining 15% to 20% of tumors represent high-grade solid nonpapillary bladder carcinoma, which arise from high-grade intraurothelial neoplasia. These tumors aggressively invade the bladder wall and have a high propensity for distant metastasis.
  
  
  OBJECTIVE
  To summarize the scientific literature and provide a clinicopathologic review of the dual-track concept of bladder carcinogenesis with its important implications.
  
  
  METHODS
  Relevant articles indexed in PubMed (National Library of Medicine) between 1974 and 2005.
  
  
  CONCLUSIONS
  Although the characteristics of papillary and nonpapillary tumors are quite dissimilar, current evidence implies that both forms of bladder cancer start as a clinically occult clonal expansion of preneoplastic lesions that occupy large areas of the bladder mucosa.
authors.affiliation: Department of Urology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Philippe E
authors.initials: PE
authors.lastname: Spiess
authors.forename: Bogdan
authors.initials: B
authors.lastname: Czerniak
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000209:etiology* / Q000473:pathology*; D002295:Carcinoma, Transitional Cell / Q000209:etiology* / Q000473:pathology*; D006801:Humans; D001749:Urinary Bladder Neoplasms / Q000209:etiology* / Q000473:pathology*; D019459:Urothelium / Q000473:pathology