Diagnostic application of hMLH1 methylation in hereditary non-polyposis colorectal cancer

Colorectal cancer (CRC) due to mismatch repair (MMR) defect has distinct characteristics among unselected CRCs. These CRCs are biologically less aggressive and, thus, showing better prognosis but less sensitive to the 5FU-based chemotherapy. CRCs with MMR defect derive from both hereditary and sporadic reasons. Germline inactivation of MMR genes (hMLH1, hMSH2, hMSH6, and hPMS2) underlies the hereditary CRC with MMR defect (Lynch syndrome) and epigenetic silencing of hMLH1 gene causes the sporadic CRC with MMR defect. Hereditary and sporadic CRC with MMR defect can be detectable by microsatellite instability (MSI) test or immunohistochemical analysis among general CRCs. Lynch syndrome can be diagnosed by the clinical criteria or by genetic test to detect pathogenic germline mutations in MMR genes. However, both clinical criteria and genetic test are inadequate for the diagnosis of Lynch syndrome. Since genetic test for the diagnosis of the Lynch syndrome is expensive and not always identify pathogenic germline mutations, effective and inexpensive screening program is desirable. Here we propose a possible application of methylation test combined with MSI or pathological analysis as an effective and a cost-saving new strategy for screening of Lynch syndrome.