Lynch Syndrome (LS) is a multi organ cancer syndrome caused by germline mutations in the four MMR genes MLH1, MSH2, MSH6 and PMS2. The tumour spectrum includes colorectal- and endometrial cancer as the predominant cancers, and carcinoma of the upper uro-epithelial tract, ovary, hepatobiliary tract, brain, stomach and prostate with lower frequency. This evidence concerns the gene MLH1 and cancer.