Compatible with previous studies showing that somatic mutations in MMR genes were frequent causes of MMR deficiency in LS-like tumors [5,6,34], half of the sporadic MSI-high tumors in our series (46/92) had somatic mutations in MMR genes after exclusion of the CIMP-positive status or MLH1 hypermethylation. This evidence concerns the gene MLH1 and mismatch repair cancer syndrome 1.