Promoter Mutation Analysis of Whole-Organ Mapping Bladder Cancers.

Background: Multifocal occurrence is a main characteristic of urothelial bladder cancer (UBC). Whether urothelial transformation is caused by monoclonal events within the urothelium, or by polyclonal unrelated events resulting in several tumor clones is still under debate. promoter mutations are the most common somatic alteration identified in UBC. In this study, we analyzed different histological tissues from whole-organ mapping bladder cancer specimens to reveal mutational status, as well as to discern how tumors develop.

Methods: Up to 23 tissues from nine whole-organ mapping bladder tumor specimens, were tested for promoter mutations including tumor associated normal urothelium, non-invasive urothelial lesions (hyperplasia, dysplasia, metaplasia), carcinoma in situ (CIS) and different areas of muscle invasive bladder cancers (MIBC). The mutational DNA hotspot region within the promoter was analyzed by SNaPshot analysis including three hot spot regions (-57, -124 or -146). Telomere length was measured by the Relative Human Telomere Length Quantification qPCR Assay Kit.

Results: promoter mutations were identified in tumor associated normal urothelium as well as non-invasive urothelial lesions, CIS and MIBC. Analysis of separate regions of the MIBC showed 100% concordance of promoter mutations within a respective whole-organ bladder specimen. Polyclonal events were observed in five out of nine whole-organ mapping bladder cancers housing tumor associated normal urothelium, non-invasive urothelial lesions and CIS where different promoter mutations were found compared to MIBC. The remaining four whole-organ mapping bladders were monoclonal for mutations. No significant differences of telomere length were observed.

Conclusions: Examining multiple whole-organ mapping bladders we conclude that promoter mutations may be an early step in bladder cancer carcinogenesis as supported by mutations detected in tumor associated normal urothelium as well as non-invasive urothelial lesions. Since mutated promoter regions within non-invasive urothelial lesions are not sufficient alone for the establishment of cancerous growth, this points to the contribution of other gene mutations as a requirement for tumor development.