The underlying cause is a germline mutation in one of the mismatch repair (MMR) genes: MLH1, MSH2 (EPCAM), MSH6 or PMS2. Mutations in all MMR genes are associated with a significantly increased cancer risk compared to the general population, although MSH6 and PMS2 carriers show lower penetrance compared to MLH1 and MSH2 carriers [1–3]. This evidence concerns the gene MLH1 and cancer.