['There is a need in urological practice to identify new bladder cancer molecular markers to further develop noninvasive diagnostic tests. We analyzed bladder cancer gene expression profiles to determine the relevant differentially expressed genes and whether this differential expression is maintained in urine samples.', 'We collected 55 tissue specimens from a total of 43 patients with bladder cancer and 12 controls, and 49 urine samples from bladder washings from a total of 36 patients with bladder cancer and 13 controls between September 2003 and December 2004. DNA microarrays (GeneChip Human Genome U133 Plus 2.0 Array) were used to identify differentially expressed genes at 3 bladder cancer stages. Selected differentially expressed genes were validated in an independent set of bladder washings by quantitative reverse transcriptase-polymerase chain reaction.', 'Unsupervised cluster analysis of DNA microarray data showed a clear distinction in control vs tumor samples and low vs high grade tumors. Genes with at least 2-fold differential expression in controls vs tumors (2,937 probe sets or 2,295 genes) and in low vs high grade tumors (674 probe sets or 530 genes) were identified and ranked. Gene expression measurements in bladder washings of the 6 most differentially expressed genes in controls vs tumors were confirmed for the 2 over expressed genes tested by quantitative reverse transcriptase-polymerase chain reaction. All 8 selected differentially expressed genes in low vs high grade tumors were confirmed in bladder washing samples.'] Does dNA microarray expression profiling of bladder cancer allow identification of noninvasive diagnostic markers?