Microsatellite instability (MSI) is a hallmark of mismatch repair (MMR)-deficient cancers including colorectal cancer (CRC). MSI represents 15% of CRCs as a result of either epigenetic silencing of MLH1 or mutations in one of the MMR
genes: MLH1, MSH2, MSH6 and PMS2. MSI tumors have a better prognosis than microsatellite stable (MSS) tumors while responding differently to treatments, including relative resistance to 5-FU and high clinical benefit from
immune checkpoint therapy. Deficient MMR can lead to deficient DNA doublestrand-break repair