1 Department of General Surgery, Peking University People's Hospital, Beijing, P. R. China.
2 Department of Retroperitoneal Tumor Surgery, Peking University International Hospital, Beijing, P. R. China.
3 Department of Gastroenterology, State Key Laboratory for Digestive Health, National Clinical Research Center for Digestive Disease, Beijing Digestive Disease Center, Beijing Key Laboratory for Precancerous Lesion of Digestive Disease, Beijing Friendship Hospital, Capital Medical University, Beijing, P. R. China.