1. Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China
2. Department of Gastroenterology, General Hospital of Central Theater Command, Wuhan, Hubei 430070, P.R. China
3. Program in Molecular Pathological Epidemiology, Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02212, USA