1. Department of Gastrointestinal Surgery, Cancer Institute Hospital, Tokyo, Japan
2. Department of Upper Abdominal Surgical Oncology, National Cancer Centre Hospital East, Chiba, Japan
3. Department of Surgery, Niigata Cancer Centre Hospital, Niigata, Japan
4. Department of Surgery, Kanagawa Cancer Centre, Kanagawa, Japan
5. Department of Surgery, Aichi Cancer Centre, Aichi Hospital, Aichi, Japan
6. Department of Surgery, Miyagi Cancer Centre, Miyagi, Japan
7. Department of Surgery, Tochigi Cancer Centre, Tochigi, Japan
8. Department of Surgical Oncology, National Cancer Centre Hospital, Tokyo, Japan
9. Department of Biostatistics/Epidemiology and Preventive Health Sciences, University of Tokyo, Tokyo, Japan