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Mutational signature profiling classifies subtypes of clinically different mismatch repair deficient tumors with a differential immunogenic response potential

Background Mismatch repair (MMR) deficiency is the hallmark of tumors from Lynch syndrome (LS), sporadic MLH1 hypermethylated, and Lynch-like syndrome (LLS), but there is a lack of understanding of the variability in their mutational profiles based on clinical phenotypes. The aim of this study was to perform a molecular characterization to identify novel features that can impact tumor behavior and clinical management. Methods We tested 105 MMR-deficient colorectal cancer tumors (25 LS, 35 LLS, and 45 sporadic) for global exome microsatellite instability, cancer mutational signatures, mutational spectrum and neoepitope load. Results 78% of tumors showed high contribution of MMR-deficient mutational signatures, high level of global exome microsatellite instability, loss of MLH1/PMS2 protein expression and included sporadic tumors. 22% of tumors showed weaker features of MMR deficiency, 73% lost MSH2/MSH6 expression and included half of LS and LLS tumors. Remarkably, 9% of all tumors lacked global exome microsatellite instability. Lastly, HLA-B07:02 could be triggering the neoantigen presentation in tumors that show the strongest contribution of MMR-deficient tumors. Conclusions Next-generation sequencing approaches allow for a granular molecular characterization of MMR-deficient tumors, which can be essential to properly diagnose and treat patients with these tumors in the setting of personalized medicine.