MSH2 is a core component of the post-replicative DNA mismatch repair (MMR) system that forms heterodimers with MSH6 (MutS alpha) or MSH3 (MutS beta) to recognize and initiate repair of DNA mismatches 1. MutS alpha specifically recognizes single base mismatches and small insertion-deletion loops, while MutS beta detects larger loops up to 13 nucleotides 2. Upon mismatch binding, MSH2-containing complexes undergo ATP-dependent conformational changes that convert them into sliding clamps capable of directing downstream MMR events including strand discrimination and resynthesis 3. Beyond canonical MMR, MSH2-MSH3 promotes DNA end resection during homologous recombination repair and blocks polymerase theta-mediated end-joining through SMARCAD1 interaction 4. Germline MSH2 mutations account for approximately 56% of pathogenic variants in Lynch syndrome families, with 72% of tumors from Amsterdam criteria-positive patients showing high microsatellite instability 5. MSH2 deficiency drives endometrial cancer through mitochondrial dysfunction and metabolic reprogramming, with 50% of MSH2-knockout mice developing endometrial cancer by 16 months 6. Clinically, approximately 90% of observed MSH2 missense variants are variants of uncertain significance; however, functional studies demonstrate 89% are functionally neutral 1. Cell-based assays enable classification of VUS to guide Lynch syndrome diagnosis and cancer risk stratification 32.