Review ArticlesColorectal Cancer Due to Deficiency in DNA Mismatch Repair Function A ReviewBellizzi, Andrew M. MD; Frankel, Wendy L. MDAuthor Information Department of Pathology, The Ohio State University Medical Center, Columbus, OH Reprints: Wendy L. Frankel, MD, Department of Pathology, The Ohio State University Medical Center, E-411 Doan Hall, 410 West 10th Avenue, Columbus, OH 43210-1218 (e-mail: [email protected]). All figures can be viewed online in color at http://www.anatomicpathology.com. Advances in Anatomic Pathology: November 2009 - Volume 16 - Issue 6 - p 405-417 doi: 10.1097/PAP.0b013e3181bb6bdc Buy Metrics Abstract Lynch syndrome (LS) is an autosomal dominant cancer predisposition syndrome attributable to deleterious germline mutations in mismatch repair (MMR) genes. The syndrome is typified by early-onset, frequently right-sided colorectal cancers (CRCs) with characteristic histologic features and tendency for multiplicity and an increased risk for extracolonic tumors at particular sites; it accounts for 1% to 5% of CRC. Deficient mismatch repair (dMMR) function manifests as immunohistochemically detectable absence of one or more MMR proteins and microsatellite instability (MSI). Approximately 15% of sporadic, noninherited CRC are characterized by high-level MSI, nearly always owing to transcriptional silencing of MLH1; these sporadic and LS cases exhibit considerable phenotypic overlap. Identification of CRC with dMMR is desirable to identify LS and because MSI status is prognostic and potentially predictive. This review will discuss the history of LS, the principles of MMR and MSI, the clinicopathologic features of LS-associated and sporadic high-level MSI CRC, the fundamentals of clinical testing for dMMR CRC, and the results of the Columbus-area Lynch syndrome study. We conclude with our approach to population-based LS screening based on institutional experience with nearly 2000 cases. © 2009 Lippincott Williams & Wilkins, Inc.