High-resolution analysis of genomic copy number alterations in bladder cancer by microarray-based comparative genomic hybridization

We have screened 22 bladder tumour- derived cell lines and one normal urothelium- derived cell line for genome- wide copy number changes using array comparative genomic hybridization ( CGH). Comparison of array CGH with existing multiplex-fluorescence in situ hybridization ( M-FISH) results revealed excellent concordance. Regions of gain and loss were defined more accurately by array CGH, and several small regions of deletion were detected that were not identified by M- FISH. Numerous genetic changes were identified, many of which were compatible with previous results from conventional CGH and loss of heterozygosity analyses on bladder tumours. The most frequent changes involved complete or partial loss of 4q ( 83%) and gain of 20q ( 78%). Other frequent losses were of 18q ( 65%), 8p ( 65%), 2q ( 61%), 6q ( 61%), 3p ( 56%), 13q ( 56%), 4p ( 52%), 6p ( 52%), 10p ( 52%), 10q ( 52%) and 5p ( 43%). We have refined the localization of a region of deletion at 8p21.2- p21.3 to an interval of approximately 1 Mb. Five homozygous deletions of tumour suppressor genes were confirmed, and several potentially novel homozygous deletions were identified. In all, 15 high- level amplifications were detected, with a previously reported amplification at 6p22.3 being the most frequent. Real- time PCR analysis revealed a novel candidate gene with consistent overexpression in all cell lines with the 6p22.3 amplicon.