1. Department of Colorectal Surgery, National Cancer Centre Hospital East, Kashiwa, Japan
2. Department of Surgery, Toho University Ohashi Medical Centre, Tokyo, Japan
3. Department of Surgery, Tokyo Metropolitan Komagome Hospital, Tokyo, Japan
4. Department of Colorectal Surgery, National Cancer Centre Hospital, Tokyo, Japan
5. Department of Colon and Rectal Surgery, Shizuoka Cancer Centre, Shizuoka, Japan
6. Department of Gastroenterological Surgery, Ishikawa Prefectural Central Hospital, Kanazawa, Japan
7. Department of Gastroenterological Surgery, National Hospital Organization Shikoku Cancer Centre, Matsuyama, Japan
8. Department of Biostatistics, Yokohama City University, Yokohama, Japan