1. Endoscopy Center, Beijing Cancer Hospital, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Peking University Cancer Hospital and Institute, Beijing 100142, P.R. China
2. Department of Gastrointestinal Surgery, Beijing Cancer Hospital, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Peking University Cancer Hospital and Institute, Beijing 100142, P.R. China