1. Department of Gastroenterology, General Hospital of Ningxia Medical University, Yinchuan, Ningxia 750000, P.R. China
2. Department of Pathology, North China University of Science and Technology Affiliated Hospital, Tangshan, Hebei 063000, P.R. China
3. Department of Gastroenterology, Ordos Center Hospital, Ordos, Inner Mongolia 017000, P.R. China