Introduction: Cigarette smoke is responsible for approximately one-half of cases of bladder cancer. The risk for developing urothelial tumours in relation with the conssumption of tobacco has shown interindividual variations. On the other hand, genome instability, which is usually expressed as a loss of heterocigosity (LOH), appart from playing a direct role in the carcinogenesis pathways of the urothelial tumours, has been suggested to modify the risk associated with exogenous agents. Since one of the most common genomic abnormalities is located in chromosome 9, within a deletion area between 9p21 and 9q34.1, we analyzed the incidence of alterations in 6 microsatellites located in chromosome 9 in patients with bladder cancer and whether those alterations show any asociation with environmental risk factors.
Materials and methods: All patients with diagnosis of bladder cancer as assessed by cystoscopy and confirmed by histological exam were included in the study.
Samples of tumoral DNA and samples of healthy bladder tissue were obteined by transurethral resetion of the bladder or cystectomy. DNA extraction was performed by cellular lysis followed by nuclei digestion of using K proteinase and phenolic extraction. D9S126, D9S736, D9S66, D9S171, D9S1793 and D9S1848 were used as the polymorphic markers for LOH analysis. 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. The threshold for LOH was set as a 50% reduction of the intensity of one allele according with the selection of tumour tissues. The results of the DNA analysis were correlated with the environmental risk factors including smoking.
Results: 69 samples of bladder tissue from 23 patients were analysed. A possitive association was found between the presence of LOH in D9S66 and smoking more than 40 cigarettes a day (p=0.0164).
Conclusions: Our results suggest that smoking shows a genomic alteration expressed as a LOH in D9S66 of chromosome 9. More studies based on molecular biology and epigenetics are needed. If our findings were proved, the developing of a genetic engineering tool for the management of bladder cancer in smokers may happen with important clinical implications in the future.