Mutation in or inactivation of mismatch repair (MMR) genes, such as MutS homolog 2 (MSH2), which causes microsatellite instability (MSI), is the most common lesion in hereditary nonpolyposis colorectal cancer (HNPCC or Lynch Syndrome) and occurs in 20% of sporadic CRC [8,15]. The gene discussed is MSH2; the disease is hereditary nonpolyposis colon cancer.