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.