Prognosis in bladder cancer is clearly worse if cancer cells reach the muscle bladder wall (stage pT2-4) compared to minimally invasion (stage pT1) where cancer cells do not go beyond lamina propria of the urinary bladder. Increased genomic instability is suspected to increase the malignant potential of cancer cells.

The aim of our study was to perform a comparative genomic hybridization for whole tumor genome scan of invasive transitional cell carcinomas of the urinary bladder of Bulgarian patients in order to compare the genomic instability of pT1 and pT2-4 invasive tumors as well as to look for specific chromosomal imbalances associated with muscle invasion.

Our results did not show significant differences in the total number of chromosomal aberrations between pT1 and pT2-4 (P=0.2030). This is consistent with models suggesting two different entities of bladder neoplasms, one (pTaG1/G2) being genetically stable with low risk of progression, and the other one (pTa G3, pT1-4) with a high degree of genetic instability and high risk of progression. Deletions were more frequent in pT2-4 almost reaching statistical significance ( mean 0.13 deletions per case in pT1 versus 1.4 in pT2-4; P=0.0610). Some of the genetic alterations were significantly linked to the tumor stage - gains at 5p, 17q and 20q (P=0.0198, P=0360 and P=0.0336 ).

In summary, our study demonstrated that not the total genome instability but specific chromosomal aberrations (5p+, 17q+ and 20q+) are associated with muscle invation of urinary bladder cancer.