Correspondence to Kaichun Wu, PhD, doctor tutor, professorof State Key Laboratory of Cancer Biology, Institute of Digestive Diseases, Xijing Hospital Fourth Military Medical University; Address: Institute of Digestive Diseases, Xijing Hospital, Fourth Military Medical University, Xi'an, Postcode: 710032; Tel.: 029-83375229; Fax: 029-82539041; E-mail: wangyiwind@126.com.