Purpose: Inactivation of the genes involved in DNA mismatch repair (MMR) is associated with microsatellite instability (MSI) and loss of heterozygosity (LOH). The aim of the current study was to assess the presence of MSI and promoter hypermethylation of MLH1 and MSH2 in Bulgarian PATIENTS WITH SPORADIC COLORECTAL CANCER (CRC) AND TO ANALYZE THEIR POSSIBLE EFFECT ON THE DEVELOPMENT, PROGRESSION AND PROGNOSIS OF THE DISEASE.
Methods: We examined MSI in 126 patients with sporadic CRC and the methylation status of the MLH1 and MSH2 promoter regions in the cases with MSI/LOH by using a panel of 5 microsatellite markers (BAT26, D5S346, D18S35, D2S123 and FGA) and methyl-specific PCR (MSP) of bisulfite converted DNA.
Results: MSI/LOH was found in 36 (28.6%) patients. Among them, 30 were analyzed for promoter hypermethylation of MLH1 and we detected hypermethylation in 15 (50%) of them, whereas promoter hypermethylation of MSH2 was observed only in one case. The presence of MSI/LOH was associated with younger age (p=0.002), more advanced stage (III/IV stage) (p=0.029), lower degree of differentiation (p=0.001), and right-sided tumor localization (p=0.0002), but not with overall survival (log rank, p=0.566).
Conclusion: Our data suggest that sporadic CRCs with MSI/LOH are more aggressive, develop earlier and progress faster to more advanced stage. The most frequent cause of failure of DNA MMR system appeared to be the hypermethylation of CpG islands of the promoter region of MLH1, whereas the methylation of MSH2 was a rare event.