BAT25, ACVR2, and TGFBR2 mononucleotide STR markers: A triplex panel for microsatellite instability testing in colorectal tumors

Microsatellite instability (MSI) in colorectal cancer (CRC) patients is considered as a diagnostic and prognostic marker. MSI is a consequence of mismatch repair deficiency which is evaluated using the different microsatellite markers on the whole genome. In this pilot study, the diagnostic value of a novel triplex panel including three mononucleotide markers has been evaluated in comparison to the standard Promega kit for MSI testing in CRC patients with Amsterdam II criteria.

DNA extracted from tumors and normal Formalin‑Fixed Paraffin‑Embedded (FFPE) tissues of index cases from 37 HNPCC (Hereditary non‑polyposis colorectal cancer) families were evaluated for MSI state. Primer design for three markers, including BAT25, ACVR2, and TGFBR2, was performed using 19 nucleotides of the M‑13 phage. The instability of each marker was assessed through fragment analysis in comparison with Promega kit markers for all patients. The sensitivity and specificity of each marker have been calculated.

The comparative evaluation of MSI in both tumors and normal adjacent FFPE tissues demonstrated a separate sensitivity as 100%, 83.3%, and 76.9% for BAT25, ACVR2, and TGFBR2, respectively, and 100% sensitivity in the form of a triplex. Moreover, the specificity for each of these three markers in MSI testing was estimated as 100%, separately and in the form of the triplex in comparison with the Promega pentaplex standard Kit.

A high sensitivity and specificity for the novel triplex panel in MSI‑testing were estimated among Iranian patients. More studies are recommended to confirm this panel as a diagnostic kit for MSI testing.