National Defense Medical College - Department of Surgery, Tokyo Medical and Dental University - Department of Translational Oncology, Shizuoka General Hospital - Division of Statistical Analysis of Research Support Center, Tokyo Medical and Dental University - Department of Specialized Surgeries, Tokyo Medical and Dental University - Department of Specialized Surgeries, Nagoya University - Department of Biostatistics, Kyoto Prefectural University of Medicine - Department of Biostatistics, Kurume University - Biostatistics Center, Ogaki Municipal Hospital - Department of Surgery, Tokyo Metropolitan Tama Medical Center - Department of Surgery, Social Insurance Tagawa Hospital - Department of Surgery, Chugoku Central Hospital - Department of Surgery, Teikyo University - Department of Surgery, Hakodate Goryokaku Hospital - Department of Surgery, Hyogo College of Medicine - Division of Lower GI Surgery and Tokyo Medical and Dental University