Consistent genomic alterations in carcinoma in situ of the urinary bladder confirm the presence of two major pathways in bladder cancer development

Abstract

Bladder cancer develops through different pathways, provisionally entitled "papillary" and "invasive." Carcinoma in situ (CIS) is thought to be the precursor of invasive bladder cancer. However, little is known about chromosomal alterations of these clinically important lesions, and the relationship between chromosomal alterations and the different pathways. We laser-microdissected 12 CIS and 4 dysplasia samples concomitant to invasive bladder cancer. We determined genome-wide chromosome copy number changes and loss of heterozygosity (LOH) using Mapping 10K SNP microarrays. We further examined 48 high-risk non-muscle-invasive bladder cancers using SNP microarrays to reveal characteristic changes correlated with the CIS-phenotype. DNA copy-number changes were further validated using QPCR in 77 independent tumor samples. CIS was found to be chromosomal unstable in 8 of 12 cases. Characteristic chromosomal changes were copy number gains of chromosomes 5p, 6p22.3, 10p15.1 and losses/LOH of chromosome 5q and 13q13-q14. Tumor samples with these alterations were significantly associated with CIS. Using FGFR3 mutations as markers of the opposing papillary phenotype, we found 5p gains and FGFR3 mutations mutually exclusive. No FGFR3 mutations were found in 23 CIS and dysplasia samples. Based on this, we classified high-risk non-muscle-invasive bladder tumors according to FGFR3 mutations and chromosomal changes into papillary and CIS-type tumors with high correlation to CIS status (p = 0.001). Furthermore, we found significant correlation to the results of molecular classifiers based on gene-expression. We concluded that chromosomal changes may be used to characterize different pathways in bladder cancer development.