1. JCOG Data Center/Operations Office, National Cancer Center Hospital, Tokyo, Japan
2. Department of Head and Neck Surgery, Aichi Cancer Center Hospital, Aichi, Japan
3. Department of Head and Neck Surgery, National Cancer Center Hospital East, Chiba, Japan
4. Department of Otolaryngology––Head and Neck Surgery, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Hokkaido, Japan
5. Department of Medical Oncology/Hematology and Cancer Center, Kobe University Hospital, Hyogo, Japan