PCR and fragment analysis of paired normal and tumor tissue to determine microsatellite instability (MSI) at the standard five NCI-recommended loci. Positive results are reported as MSI-high (at least two markers are unstable) or MSI-low (one marker is unstable).
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.
- Note: An additional patient sample from normal, non-tumor tissue is required for comparison testing in MSI Analysis. Please submit all specimens with one test requisition form.
- Specimen requirements for normal tissue in order of preference are: 1) 5 mL peripheral blood in EDTA tube OR 2) FFPE tissue slides or block containing only non-tumor tissue. Please label these as "normal tissue". OR 3) In cases where no alternative tissue is available, we can attempt to isolate non-tumor tissue from the tumor specimen submitted. Note "Use tumor sample for normal tissue" on requisition. See requirements below.
- Specimen requirements for tumor tissue: FFPE 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 and/or blood, making sure cold pack is not in direct contact with specimen. Slides can be packed at room temperature.