[Identification and management of patients with Lynch syndrome]

About 5% of colorectal cancer (CRC) cases occurred in the context of an underlying hereditary predisposition syndrome. Lynch syndrome is the main causes of hereditary CRC but is also associated with a higher risk of other cancers (such as endometrial cancer and ovarian cancer). It is the consequence of constitutional mutation in a MisMatch Repair (MMR) gene, involved in DNA repair: MLH1, MSH2, MSH6 or PMS2; or of the EPCAM gene (MSH2 promotor). If a mutation predisposing to Lynch Syndrome is identified in an individual, special monitoring should be initiated, adapted to estimated cancer risk. Clinical criteria (Amsterdam II and Bethesda) have been validated to identify the patients who should be referred for genetic counseling in order to initiate constitutional DNA testing. Furthermore, the French National Cancer Institute (INCa) systematically recommend tumoral testing looking for MMR system failure in case of CRC diagnosed under 60, endometrial cancer diagnosed under 50 or whatever the age in patients diagnosed with CRC or endometrial cancer harbouring personal or familal history of Lunch Syndrome cancers. In this review, we will discuss how to detect Lynch syndrome (identification of the index case and family screening) and how to monitor it in 2019.