A DLBCL with microsatellite instability was reported in a colorectal cancer patient with a germline MLH1 mutation.17 Although DLBCL may not be prominent in Lynch syndrome,18 hematological malignancies including DLBCL have a prevalence of 15%19 in constitutional mismatch repair deficiency resulting from bi-allelic germline mutations in one of the four MMR genes MLH1, MSH2, MSH6 or PMS2. 20. This evidence concerns the gene MLH1 and mismatch repair cancer syndrome 1.