Lynch syndrome in the 21st century: clinical perspectives

Lynch syndrome (LS) is the most common of all inherited cancer syndromes, associated with substantially elevated risks for colonic and extracolonic malignancies, earlier onset and high rates of multiple primary cancers. At the genetic level, it is caused by a defective mismatch repair (MMR) system due to presence of germline defects in at least one of the MMR genes- MLH1, MSH2, MSH6, PMS2 or EPCAM. An impaired MMR function during replication introduces infidelity in DNA sequence and leads to ubiquitous mutations at simple repetitive sequences (microsatellites), causing microsatellite instability (MSI). Although previously, clinicopathological criteria such as Amsterdam I/II and Revised Bethesda Guidelines were commonly used to identify suspected LS mutation carriers, there has been a recent push towards universally testing, especially in case of colorectal cancers (CRCs), through immunohistochemistry for expression of MMR proteins or through molecular tests (polymerase chain reaction, PCR) for MSI, in order to identify LS mutation carriers and subject them to genetic testing to ascertain the specific gene implicated. In this review, we have discussed the latest diagnostic strategies and the current screening and treatment guidelines for colonic and extracolonic cancers in clinically affected and at-risk individuals for LS.