PCR and fragment analysis of 13 microsatellite loci are performed on macrodissected FFPE tumor tissue to detect microsatellite instability (MSI). Normal tissue is analyzed in parallel with tumor tissue when available. Minimum required tumor content is 20% when matching normal tissue is analyzed. In the absence of normal tissue, minimum required tumor content is 20% for colon tumors and 40% for other tissue types. Results are reported as MSI-high, MSI-low, or MSI-stable
MSI analysis and/or mismatch repair (MMR) IHC is recommended for all new colorectal cancer diagnoses to detect patients at increased risk of carrying germline mutations associated with Lynch Syndrome (HNPCC). MSI is also detected in sporadic colorectal cancer and its presence may imply better prognosis. MSI and MMR testing also serve as companion diagnostic tests in a wide range of solid tumors for selection of certain immuno-oncology therapies.
FFPE solid tumor tissue: Paraffin block is preferred. Alternatively, send 1 H&E slide plus 5-10 unstained slides cut at 5 or more microns. Please use positively-charged slides and 10% NBF fixative. Do not use zinc fixatives.
Use cold pack for transporting block, making sure cold pack is not in direct contact with specimen. Slides can be packed at room temperature.