MLH1 and neoplasm: MSI-H/dMMR tumor are attributed as hereditary—arising from germline mutations in one of the four mismatch repair (MMR) genes (MLH1, MSH2, MSH6, PMS2) as part of the hereditary non-polyposis colorectal cancer (HNPCC) syndrome (2, 3)—or as sporadic, arising from globally hypermethylated colorectal cancer tumors featuring loss of gene expression of MLH1 due to promoter hypermethylation (4).