Mechanistic investigations using in vitro system have shown that treatment of hMLH1-methylated colon cancer cell lines with the demethylating agent 5aza-2deoxycytidine (5-aza-dC) restores hMLH1 expression and subsequently renders the cells MMR proficient (Herman et al, 1998). This evidence concerns the gene MLH1 and malignant colon neoplasm.