Dual-track pathway of bladder carcinogenesis: practical implications.

CONTEXT: 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. DATA SOURCES: 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.