Microsatellite instability (MSI) results from an accumulation of insertion or deletion of repeating units during DNA replication in tumor cells with a deficient mismatch repair (MMR) system. MSI status is associated with response/resistance to certain immune checkpoint inhibitors. Q2 Solutions MSI assay utilizes multiplex, fluorescent PCR and capillary electrophoresis to enable sensitive detection of five mononucleotide repeat markers (BAT-25, BAT-26, NR-21, NR-24 and MONO-27)1 in tumor FFPE specimens. Microsatellite instability at two or more mononucleotide loci is interpreted as MSI-High; microsatellite instability at a single mononucleotide locus is interpreted as MSI-Low; no instability at any of the loci tested is interpreted as microsatellite stable (MSS).
Example of Colon Cancer FFPE Tissue Specimen Demonstrating MSI-High Status
Example capillary electropherogram demonstrating refer- ence, normal profile in normal tissue (upper panel) and MSI-High profile in tumor FFPE tissue (lower panel). New MSI events labeled 1−5 are detected in tumor tissue.
|MSI Assay Specifications
||BAT-25, BAT-26, MONO-27, NR-21, and NR-24 microsatellite loci
||Tumor: 3 x 5um FFPE tumor slides or 3 curls or FFPE block or DNA. Minimum 20% neoplastic cellularity required. Normal: either whole blood (1-3 mL, K2EDTA) or tumor FFPE slides with clearly indicated normal tissue area or 3 x 5um normal tissue FFPE slides, curls or block. If H&E stained slide with indicated tumor normal areas is not available, will perform H&E assessment and determine specimen adequacy.
||MSI Analysis System (Promega)2
||Thermo Fisher Scientific SeqStudio
||RUO, GCP, consult for CLIA availability
||MSI Status report. Exact number of MSI markers available as custom report.
1Boland et al. Cancer Res. 1998;58:5248-5257. 2 Promega MSI assay also available in Q² Solutions’ Beijing, China Laboratory facility.