1. Cancer Institute; the Fourth Hospital of Hebei Medical University; Shijiazhuang China
2. Department of Endoscope; the Fourth Hospital of Hebei Medical University; Shijiazhuang China
3. Department of Pathology; the Fourth Hospital of Hebei Medical University; Shijiazhuang China
4. Department of Epidemiology and Endoscope; Shexian Cancer Institute; Shexian China