Microsatellite instability testing (MSI)

Microsatellite instability (MSI) is a form of genomic instability which arises when the DNA mismatch repair (MMR) is not functioning normally. DNA mismatch repair (MMR) is a system for recognizing and repairing erroneous insertions, deletions and mis-incorporation of bases that can occur during DNA replication and recombination. The presence of MSI represents phenotypic evidence that MMR is not functioning normally which often occurs in tumor cells.