Tumor Testing and Genetic Analysis to Identify Lynch Syndrome Patients in an Italian Colorectal Cancer Cohort

SIMPLE SUMMARY: Lynch syndrome (LS) is an inherited genetic condition caused by germline mutations in DNA mismatch repair (MMR) genes. It is associated with a predisposition to different types of cancer, including colorectal cancer (CRC). CRC is the fourth most common cancer worldwide. The screening algorithm for the selection of LS patients is based on the identification of CRC specimens that have MMR loss/high microsatellite instability (MSI-H) and are wild-type for BRAF(V600). The aim of this retrospective study was to clinically and molecularly characterize CRC patients with these features. We used a comprehensive approach including tumor testing for the assessment of MSI status, clinical evaluation of patients and their families, and genetic analysis to identify variants in MMR and other cancer-related genes. The clinical and molecular characterization of these patients highlights the importance of personalized medicine to provide tailored genetic counseling, management, and surveillance to families with LS and hereditary cancer. ABSTRACT: Lynch syndrome (LS) is an inherited cancer susceptibility syndrome caused by germline mutations in a DNA mismatch repair (MMR) gene or in the EPCAM gene. LS is associated with an increased lifetime risk of colorectal cancer (CRC) and other malignancies. The screening algorithm for LS patient selection is based on the identification of CRC specimens that have MMR loss/high microsatellite instability (MSI-H) and are wild-type for BRAF(V600). Here, we sought to clinically and molecularly characterize patients with these features. From 2017 to 2023, 841 CRC patients were evaluated for MSI and BRAF(V600E) mutation status, 100 of which showed MSI-H. Of these, 70 were wild-type for BRAF(V600). Among these 70 patients, 30 were genetically tested for germline variants in hereditary cancer predisposition syndrome genes. This analysis showed that 19 of these 30 patients (63.3%) harbored a germline pathogenic or likely pathogenic variant in MMR genes, 2 (6.7%) harbored a variant of unknown significance (VUS) in MMR genes, 3 (10%) harbored a VUS in other cancer-related genes, and 6 (20%) were negative to genetic testing. These findings highlight the importance of personalized medicine for tailored genetic counseling, management, and surveillance of families with LS and other hereditary cancer syndromes.