This oncogenic pathway results from the loss of function of the dMMR genes, most often of sporadic origin (80% of cases) by somatic inactivation of the MLH1 gene (hypermethylation of the MLH1 gene promoter), more rarely with genetic harbouring of a deleterious germline mutation in one of the four MMR genes associated with the Lynch syndrome [47]. Here, MLH1 is linked to Lynch syndrome.