Test Details: Microsatellite Instability is the accumulation of insertion or deletion errors at microsatellite repeat sequences in cancerous cells as a result of a deficiency within one or more major DNA mismatch repair proteins (dMMR). PCR and fragment analysis of 5 microsatellite loci are performed on FFPE tumor tissue to detect microsatellite instability (MSI). Normal tissue is analyzed in parallel with tumor tissue. Minimum required tumor content is 20%. Microsatellite instability testing (MSI testing) measures the ability of a cell to repair mistakes in DNA replication.