MT1XT20 Single Quasi-Monomorphic Mononucleotide Marker for Detection of Microsatellite Instability in Iranian Patients with Hereditary Nonpolyposis Colorectal Cancer (HNPCC)

Colorectal malignancies with high microsatellite instability (MSI-H), either hereditary or sporadic, demonstrate better prognosis, altered response to fluorouracil (5FU) chemotherapy and altered operative approach. It is now recommended to perform MSI testing for all new cases of colorectal cancers regardless of being categorized as hereditary or sporadic. This study aimed to evaluate MT1XT20 mononucleotide marker in Iranian patients with hereditary nonpolyposis colorectal cancer (HNPCC). The samples were further characterized using Promega five-marker MSI testing panel and immunohistochemical (IHC) technique. MT1XT20 mononucleotide marker and commercially available kit (Promega, USA) incorporating five quasi-monomorphic markers were studied in 20 cases of HNPCC using polymerase chain reaction (PCR) technique. IHC was performed to evaluate the status of all four important mismatch repair (MMR) proteins, too. Eight (40%), seven (35%) and five (25%) cases showed MSI using Promega kit, IHC and MT1XT20, respectively. Among the markers included in Promega kit, BAT26 marker with instability in all 8 samples (100%) was the most instable marker. NR24 and NR21 markers showed instability in 7 cases (87.5%); BAT25 and MONO 27 markers were instable in 6 (75.0%) and 5 (62.5%) specimens, respectively. Although MT1XT20 is considered as a valid single marker in Italian population, it seems this is not hold true about the Iranian patients. Instead, BAT26 among the markers included in Promega MSI testing was shown instability in all 8 samples of MSI-H colorectal cancer (CRC). Therefore, it may be concluded that BAT26 alone is as efficient as the cohort of five markers in Iranian patients.