tumor microsatellite instability and clinicopathologic features in iranian colorectal cancer patients at risk for lynch syndrome

background: microsatellite instability (msi) is a mutational signature that is the hallmark of lynch syndrome, and msi testing is a cost-effective method to screen the disease. since there is no enough data about msi status and associated clinicopathologic features of hereditary nonpolyposis colorectal cancer (hnpcc) in iran, our study is a new trial to describe them in center of iran (isfahan). materials and methods: it is a descriptive retrospective study to screen hnpcc families using amsterdam ii criteria in central iran within 2000-2013. for msi testing, we used a commercially available kit evaluating mononucleotide markers (bat-25, bat-26, mon0-27, nr-21 and nr-24). after a fluorescent multiplex polymerase chain reaction amplification of the markers,samples were sequenced to fragment analysis. data analysis was performed using spss 16 software (spss inc., chicago, il, usa). results: overall, 31 of 45 screened hnpcc families were eventually included to msi testing. totally, 9/31 patients (29.0%) showed msi in their tumor tissues. bat-26 was the most instable marker with instability in 7/24 msi tumors (29.2%). the mean age at diagnosis in microsatellite stable (mss), msi-low (msi-l), and msi-high (msi-h) probands was respectively 44.7 (standard deviation [sd]= 11.83), 51.7 (sd = 16.17), and 36.0 (sd = 3.41) years. the most common tumor sites in mss, msi-l, and msi-h probands were rectosigmoid (~72.8%), rectum (66.7%) and right colon (50.0%), respectively. of 186 cancer patients among 31 hnpcc families,86 patients (46.2%) had colorectal cancer (crc) and 100 patients (53.8%) had extracolonic cancers. the average of crc affected members among mss, msi-l, and msi-h groups of our hnpcc families was 2.2 (sd = 1.30), 3.3 (sd = 3.21), and 4.7 (sd = 2.42)patients per family, respectively. stomach with 18.3% and 26.7% of all extracolonic cancers were most common involved organ in mss and msi-h families, respectively. conclusion: our different molecular results could be suggested to describe hnpcc families based on some new molecular mechanisms leading to mss hnpcc phenotypes. meanwhile, more evaluations within our population are recommended.