Dinucleotide microsatellite repeats are essential for the diagnosis of microsatellite instability in colorectal cancer in Asian patients

AIM: The molecular diagnosis of microsatellite instability (MSI) in colorectal cancer (CRC) is based on the analysis of five microsatellite markers. Among them, the two mononu-cleotide microsatellite repeats are considered more informative for this analysis than the three dinucleotide ones. The aim of this study is to establish the most relevant markers for MSI analysis in colorectal cancers from Asian patients. METHODS: The MSI analysis of 143 CRC cases in a routine molecular diagnostic laboratory was reviewed. Analysis by fluorescence-based PCR of the five recommended microsatellites was performed, followed by data interpretation according to internationally accepted guidelines. The results were analyzed to address (1) the rate of success in the analysis of histopathological samples not specifically prepared for molecular analysis; (2) the relative importance of individual markers in the diagnosis of high-MSI (H-MSI). RESULTS: MSI analysis was unsuccessful in 34 cases (24%), but for tissues archived in recent years the unsuccessful rate was 5%. We found the D2S123 marker the most vulnerable to inadequate tissue preservation, failing to amplify in 58 instances. Approximately 30% (32/109) of the cases were H-MSI, while 7/109 (6%) were low-MSI. A detailed analysis of the H-MSI cases revealed that the dinucleotide repeats (and D5S346 in particular) were more relevant than the mononucleotide repeats in assigning the correct MSI status. CONCLUSION: The analysis of dinucleotide repeats is essential for the establishment of MSI status in Asian CRC patients.