The authors thank Dr. Koji Komori (Department of Gastroenterological Surgery, Aichi Cancer Center Hospital, Aichi), Dr. Akio Shiomi (Division of Colon and Rectal Surgery, Shizuoka Cancer Center Hospital, Shizuoka), Dr. Masashi Ueno (Department of Gastroenterological Surgery, Cancer Institute Hospital of the Japanese Foundation for Cancer Research, Tokyo), Dr. Masaaki Ito (Department of Colorectal Surgery, National Cancer Center Hospital East, Chiba), Dr. Koya Hida (Department of Surgery, Kyoto University Hospital, Kyoto), Dr. Seiichiro Yamamoto (Department of Gastroenterological Surgery, Tokai University School of Medicine, Kanagawa), Dr. Manabu Shiozawa (Department of Gastrointestinal Surgery, Kanagawa Cancer Center, Kanagawa), Dr. Yukihide Kanemitsu (Department of Colorectal Surgery, National Cancer Center Hospital, Tokyo), Dr. Hideki Ueno (Department of Surgery, National Defense Medical College, Saitama), Dr. Tatsuya Kinjo (Department of Digestive and General Surgery, Graduate School of Medicine, University of Ryukyus, Okinawa,), Dr. Kotaro Maeda (International Medical Center, Fujita Health University Hospital, Aichi), Dr. Junichiro Kawamura (Department of Surgery, Kindai University Faculty of Medicine, Osaka), Dr. Fumihiko Fujita (Department of Surgery, Kurume University School of Medicine, Fukuoka), Dr. Keiichi Takahashi (Department of Surgery, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo), Dr. Tsunekazu Mizushima (Department of Gastroenterological Surgery, Graduate School of Medicine, Osaka University, Osaka), Dr. Yasuhiro Shimada (Department of Clinical Oncology, Kochi Health Sciences Center, Kochi), Dr. Shin Sasaki (Department of Coloproctological Surgery, Japanese Red Cross Medical Center, Tokyo), Dr. Eiji Sunami (Department of Surgery, Kyorin University Faculty of Medicine, Tokyo), Dr. Fumio Ishida (Digestive Disease Center, Showa University Northern Yokohama Hospital, Kanagawa), Dr. Keiji Hirata (Department of Surgery1, School of Medicine, University of Occupational and Environmental Health, Fukuoka), Dr. Shinobu Ohnuma (Department of Surgery, Tohoku University Graduate School of Medicine, Miyagi), Dr. Kimihiko Funahashi (Department of Gastroenterological Surgery, Toho University Omori Medical Center, Tokyo), Dr. Jun Watanabe (Department of Surgery, Gastroenterological Center, Yokohama City University Medical Center, Kanagawa), Dr. Yusuke Kinugasa (Department of Gastrointestinal Surgery, Tokyo Medical and Dental University, Tokyo), Dr. Shigeki Yamaguchi (Department of Gastroenterological Surgery, Saitama Medical University International Medical Center, Saitama), Dr. Yojiro Hashiguchi (Department of Surgery, Teikyo University School of Medicine, Tokyo), Dr. Masataka Ikeda (Division of Lower Gastrointestinal Surgery, Department of Surgery, Hyogo College of Medicine, Hyogo), Dr. Takeshi Sudo (Department of Gastroenterological Surgery, Yamagata Prefectural Central Hospital, Yamagata), Dr. Yoshito Komatsu (Department of Cancer Center, Hokkaido University Hospital, Hokkaido), Dr. Keiji Koda (Department of Surgery, Teikyo University Chiba Medical Center, Chiba), Dr. Kazuhiro Sakamoto (Department of Coloproctological Surgery, Juntendo University Faculty of Medicine, Tokyo,), Dr. Masazumi Okajima (Department of Surgery, Hiroshima City Hiroshima Citizens Hospital, Hiroshima), Dr. Hideyuki Ishida (Department of Digestive Tract and General Surgery, Saitama Medical Center, Saitama Medical University, Saitama), Dr. Yuichi Hisamatsu (Department of Surgery and Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka), Dr. Taiki Masuda (Department of Surgery, Tokyo Metropolitan Hiroo Hospital, Tokyo), Dr. Shinichiro Mori (Department of Digestive Surgery, Breast and Thyroid Surgery, Graduate School of Medicine and Dental Sciences, Kagoshima University, Kagoshima), Dr. Kazuhito Minami (Department of Surgery, Matsuyama Red Cross Hospital, Ehime), Dr. Seiji Hasegawa (Department of Surgery, Saiseikai Yokohamashi Nanbu Hospital, Kanagawa), Dr. Shungo Endo (Department of Coloproctology, Aizu Medical Center, Fukushima Medical University, Fukushima), Dr. Akinori Iwashita (Department of Pathology, Fukuoka University Chikushi Hospital, Fukuoka), Dr. Madoka Hamada (Division of Gastrointestinal Surgery, Kansai Medical University Hospital, Osaka), Dr. Koichiro Usuku and Dr. Tokunori Ikeda (Department of Medical Information Sciences and Administration Planning, Kumamoto University Hospital, Kumamoto), Dr. Kenichi Sugihara (Tokyo Medical and Dental University, Tokyo), Japanese Society for Cancer of the Colon and Rectum Committee (JSCCR) members. This study was conducted as part of JSCCR's research on the pathophysiology and staging of anal canal cancer.