1. Department of Otolaryngology-Head and Neck Surgery, Hokuto Hospital, Obihiro, Hokkaido, Japan
2. Department of Otolaryngology-Head and Neck Surgery, Asahikawa Medical University, Asahikawa, Hokkaido, Japan
3. Department of Pathology, Hokuto Hospital, Obihiro, Hokkaido, Japan
4. Keio Cancer Center, Keio University School of Medicine, Tokyo, Japan