 The WRN protein helicase is important in homologous recombinational DNA repair and also has roles in non-homologous end joining DNA repair and base excision DNA repair.A 2006 retrospective study, with long clinical follow-up, was made of colon cancer patients treated with the topoisomerase inhibitor irinotecan.In this study, 45 patients had hypermethylated "WRN" gene promoters and 43 patients had unmethylated "WRN" promoters.