Introduction: One of the hallmarks of malignant bladder neoplasms is genome instability tthrough alterations of particular microsatellite loci expressed as a loss of heterocigosity (LOH). One of the most common abnormalities is located in chromosome 9. We analyzed the incidence of alterations in 6 microsatellites located in chromosome 9 in patients with bladder cancer and whether those alterations influence the oncologic prognosis.
Materials and methods: All patients with histological diagnosis of bladder cancer were included.
Samples of tumoral DNA and healthy bladder tissue were obteined by transurethral resection of the bladder or cystectomy. DNA extraction was performed by cellular lysis followed by digestion of the nuclei using K proteinase and phenolic extraction. D9S126, D9S736, D9S66, D9S171, D9S1793 and D9S1848 were used as the polymorphic markers. The amplified products were separated by vertical electrophoresis. Detection of microsatellites abnormalities was performed using silver nitrate staining. A densitometric analysis was performed and variation in the ratio between allele-specific combinations was corrected by normal DNA matching the alleles for all markers. The results of the DNA analysis were correlated with tumoural features in terms of risk group phenotype, tumour size and TNM classification of the stage.
Results: 69 samples of bladder tissue from 23 patients were analysed testing 3 microsatellite markers located on chromosome 9p and 3 on 9q. An association between the presence of LOH in at least one of the following microsatellites: D9S66, D9S1793 or D9S171 and the existence of a high risk bladder cancer phenotype was found (p=0,0096). The LOH within some of the markers was also associated with the existence of a bladder tumour of more than 2 cm (p=0,0096). Furthermore, an association between the presence of LOH in D9S1793 and infiltrating vesical cancer has been registered (p=0.0164).
Conclusions: The results of the study suggest that patients with LOH in at least one of the markers; D9S171, D9S66 and D9S1793, have a more aggressive bladder cancer and a larger tumour. The LOH in microsatellite D9S1793 is related with the presence of an infiltrating vesical neoplasm. Markers like these that show a strong association with agressivity will identify those tumours that are likely to progress to invasive bladder cancer. The clinical implications of our findings could be very relevant in terms of follow up paterns and management decision.