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Microsatellite Instability (MSI) Assay

MSI assay utilizing multiplex, fluorescent PCR and capillary electrophoresis to enable sensitive detection of five mononucleotide repeat markers

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
Markers BAT-25, BAT-26, MONO-27, NR-21, and NR-24 microsatellite loci
Specimen Requirements 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.
Assay Method MSI Analysis System (Promega)2
System Compatibility Thermo Fisher Scientific SeqStudio
Regulatory Tier RUO, GCP, consult for CLIA availability
Deliverables 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.

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