Determination of Tumor Msi Status Without the Need For Matching Normal Dna By Analysis of Quasimonomorphic Markers in Iranian Crc Patients

Background and aim: microsatellite instability (msi), caused by defective dna mismatch repair (mmr) system, is one of the most studied biological characteristics of colorectal cancer (crc). msi is specific of hereditary nonpolyposis colorectal cancer (lynch syndrome) but is also found in 15-20% of sporadic crc. although, it is the well-known clinicopathological feature of crc, it can also occur in different type of human tumors. msi testing is recommended for most individuals newly diagnosed with crc, both for screening of lynch syndrome and for prediction of the clinical outcomes of the patients. in addition, msi also serve as screening test in non-crc tumors for selection of certain chemo-immunotherapy. bethesda panel included two mononucleotide (bat-25 and bat-26) and three dinucleotide (d5s346, d2s123, and d17s250) repeats are proposed for uniform determination of msi status in individuals suspected for lynch syndrome. however, it is recently recommended that dinucleotide repeats should be replaced by mononucleotide repeats for msi testing. therefore in this study, we evaluate a panel of five quasimonomorphic markers (nr-27, nr-21, nr-24, bat-25 and bat-26) to determine msi status in iranian crc patients and examined whether it could be used for msi determination without the need for matching normal dna. the obtained results were compared with the commercially available promega kit. methods: the msi detection using pcr based method with primers specific for quasimonomorphic markers was performed on a set of ffpe tissues from crc patients(n = 100) consisting of 24 msi-h, 26 mss, and 50 matched normal samples. results: the results obtained by pentaplex pcr reactions with quasimonomorphic markers and commercially available promega kit were compatible in all of the cases, our results demonstrated that the pentaplex pcr assay performed only in the tumor tissues is highly reproducible and accurate as compared to commercially available promega kit (correlation: 100%; kappa: 1; p <0.001). conclusion: our findings showed that tumor msi status can be established by the pentaplex pcr reaction for iranian crc patients without the need for matching normal dna.