Pathological diagnosis experience and literature review of four cases suspected Lynch-like syndrome.

Background: Among CRC patients with mismatch repair protein deficiency or microsatellite instability (MSI), up to 50% of cases lack germline mutations in MMR genes, Methods: Four cases of suspected Lynch-like syndrome encountered in daily clinical pathological diagnostic work were reported. The histopathological characteristics and molecular pathological changes of related tumors were analyzed, and the diagnosis and treatment progress of this disease were reviewed via literature. Results: Combined with clinical findings and molecular pathological tests, 2 cases were diagnosed as Lynch-like syndrome (LLS), and 2 case was diagnosed as Lynch syndrome with atypical phenotype. Lynch-like syndrome-related tumors can occur in the colorectum and extraintestinal organs. Colorectal tumors show no specific locational or histological features, while extraintestinal tumors often exhibit poor differentiation and abundant interstitial lymphocyte infiltration. Patients with Lynch-like syndrome all exhibit tumoral lesions with loss of MMR protein (MLH1, PMS2, MSH2, MSH6) expression, microsatellite instability (MSI-L/MSI-H), wild-type Conclusion: Extraintestinal tumors associated with Lynch-like syndrome mostly exhibit histopathological characteristics and MMR/MSI changes similar to classic Lynch syndrome, but without pathogenic germline MMR mutations or