1. Department of Gastroenterology, Hirosaki University Graduate School of Medicine, Japan
2. Sawada Clinic of Internal Medicine, Japan
3. Komai Clinic of Gastroenterology and Internal Medicine, Japan
4. Sasaki Clinic of Gastroenterology and Internal Medicine, Japan
5. Chiba Clinic of Gastroenterology and Internal Medicine, Japan
6. Shinjo Clinic of Gastroenterology and Internal Medicine, Japan
7. Department of Cancer Epidemiology and Community Health, Hirosaki University Hospital, Japan