Mutation, deletion, or promoter methylation of these MMR genes is present in approximately 12% of ovarian cancers, 15% of colorectal cancer, 22% of gastric cancers, and up to 30% of endometrial cancers, as well as heritable cancer syndromes, such as Lynch syndrome (monoallelic germline mutation of an MMR gene) and constitutional mismatch repair deficiency (CMMRD; biallelic germline mutation of an MMR gene), which have an increased risk of numerous cancers [40, 84, 105, 106]. This evidence concerns the gene MRC1 and Lynch syndrome.