Although MMR deficiency is the hallmark of Lynch syndrome, 10–15% of MMR-deficient CRCs are not Lynch syndrome, being this deficiency caused by (i) somatic methylation of the MLH1 promoter, usually associated with BRAF somatic mutations; or (ii) double somatic mutations in the MMR genes, which explains the majority of Lynch-like cases [24], i.e., patients with an MMR deficient tumor with no identified germline pathogenic variant in an MMR gene and no somatic MLH1 promoter methylation [25]. This evidence concerns the gene MRC1 and Lynch syndrome.