MLH1 and neoplasm: DNA promoter hypermethylation is often an early event in tumorigenesis and is commonly observed in tumor-suppressor genes, such as cyclin-dependent kinase inhibitor 2A (CDKN2A), breast cancer gene 1 (BRCA1), and MutL protein homolog 1 (MLH1), among others, where excessive methylation represses transcription, ultimately disabling cell-cycle barriers that normally limit cell proliferation and compromising the cellular functions that are crucial for maintaining genomic stability and repair [120,121,122,123].