1. Department of Toxicology, School of Public Health, Lanzhou University, Lanzhou, Gansu 730000, P.R. China
2. Department of Gastroenterology, Third People's Hospital of Gansu Province, Lanzhou, Gansu 730000, P.R. China
3. Department of Gastrointestinal Surgery, Gansu Wuwei Tumor Hospital, Wuwei, Gansu 733000, P.R. China