Hereditary non-polyposis colorectal cancer (HNPCC) or Lynch syndrome is an autosomal dominant disease primarily associated with germline mutations in DNA mismatch repair genes. HNPCC accounts for 2-3% of all colorectal cancer. Approximately 70-80% of HNPCC cases result from defects in MLH1 and MSH2. Mutations in MLH1 affect the MLH1-PMS2 complex formation and may cause defects in the DNA error repair mechanism.