Incidence and molecular characteristics of deficient mismatch repair conditions across nine different tumors and identification of germline variants involved in Lynch-like syndrome

Based on molecular characteristics, deficient DNA mismatch repair (dMMR) solid tumors are largely divided into three categories: somatically MLH1-hypermethylated tumors, Lynch syndrome (LS)-associated tumors, and Lynch-like syndrome (LLS)-associated tumors. The incidence of each of these conditions and the corresponding pathogenic genes related to LLS remain elusive. We identified dMMR tumors in 3609 tumors from 9 different solid organs, including colorectal cancer, gastric cancer, small-bowel cancer, endometrial cancer, ovarian cancer, upper urinary tract cancer, urinary bladder cancer, prostate cancer, and sebaceous tumor, and comprehensively summarized the characterization of dMMR tumors. Characterization of dMMR tumors were performed as loss of at least one of MMR proteins (MLH1, MSH2, MSH6, and PMS2), by immunohistochemistry, followed by MLH1 promotor methylation analysis and genetic testing for MMR genes where appropriate. Somatic variant analysis of MMR genes and whole exome sequencing (WES) were performed in patients with LLS. In total, the incidence of dMMR tumors was 5.9