Lynch Syndrome: An Update of Underlying Molecular Mechanisms, Phenotypes and Methods to Classify Variants of Uncertain Significance

In 2022, colorectal cancer (CRC) was the third most common type of cancer worldwide and the second most common in Europe. CRC ranked as the second leading cause of cancer-related deaths both worldwide and in Europe, with 904,019 and 247,966 deaths, respectively. The majority of CRC cases are sporadic (60–75%); however, 10–35% of CRC are estimated to result from the interaction of heritable and environmental factors. Among these, 5–6% are caused by inherited variants in genes that predispose to the development of CRC. Among the known inherited causes, Lynch Syndrome (LS), formerly known as Hereditary Nonpolyposis Colorectal Cancer (HNPCC), is the most frequent and accounts for approximately 3% of all CRC. Here we review and update on multiple aspects of LS in the context of CRC, including its genetic and molecular basis, current guidelines for molecular screening and variant classification. Furthermore, we review functional assays that have been used to determine the biological impact of genetic variants of uncertain significance (VUS) and discuss future perspectives in the field.