Genetic modeling of human urinary bladder carcinogenesis

We developed a model of human urinary bladder cancer progression from in situ precursor lesions to invasive carcinoma using whole organ histologic and genetic mapping. The model represents a high-density and detailed analysis regarding allelic losses on chromosomes 4, 8, 9, 11, and 17 as revealed by testing of 234 samples obtained from five cystectomy specimens. The samples corresponded to microscopically identified intraurothelial precursor conditions ranging from dysplasia to carcinoma in situ and invasive cancer. The initial analysis of paired normal and tumor DNA samples disclosed allelic losses in 72 of 225 tested hypervariable DNA markers. Subsequent use of these markers on all mucosal samples revealed that 47 had alterations with a statistically significant relation to urothelial neoplasia. The allelic losses clustered in 33 distinct chromosomal regions, indicating the location of putative tumor suppressor genes involved in the development and progression of urinary bladder cancer. Some of the markers with statistically significant allelic losses mapped to the regions containing well-characterized tumor suppressor genes but many were located in previously unknown loci. The majority of statistically significant allelic losses (70%) occurred early in low-grade intraurothelial dysplasia, and some of them involved adjacent areas of morphologically normal mucosa preceding the development of microscopically recognizable precursor lesions. The remaining 30% of markers developed allelic losses in the later phases of urothelial neoplasia, implicating their involvement in progression to invasive disease. Markers exhibiting allelic losses in early phases of urothelial neoplasia could be used for detection of occult preclinical or even premicroscopic phases of urinary bladder cancer, whereas markers that showed allelic losses in the later phases of the process could serve as indicators of progression to invasive disease. The approach used in this study facilitates genome-wide modeling of cancer progression and provides important chromosomal landmarks for more specific studies of multistep urinary bladder carcinogenesis.