Microsatellite instability (MSI) is a condition characterized by alterations in the length of microsatellites due to a failure in the DNA mismatch repair (MMR) system. This leads to an accumulation of insertion or deletion errors in microsatellite regions of the genome, which are short, repetitive sequences of DNA. MSI is a hallmark of certain types of cancer and is particularly prevalent in colorectal cancer, endometrial cancer, and gastric cancer.
