 Epigenetic gene silencing of DNA repair genes occurs frequently in NSCLC.At least nine DNA repair genes that normally function in relatively accurate DNA repair pathways are often repressed by promoter hypermethylation in NSCLC (see table).One DNA repair gene, "FEN1", that functions in an inaccurate DNA repair pathway, is expressed at an increased level due to hypo-, rather than hyper-, methylation of its promoter region (deficiency of promoter methylation) in NSCLC (see table).