Approximately 15% of CRC development is based on microsatellite instability (MSI-H) due to either germline mutations in one of the mismatch repair genes MLH1, MSH2, MSH6, and pMSM2 (Lynch Syndrome), or to sporadic mutations in the DNA mismatch repair pathway which predominantly occurs through hypermethylation of the MLH1 promotor region and is often associated with the BRAFV600E mutation (reviewed in [8, 9]). The gene discussed is MLH1; the disease is Lynch syndrome.