1. Department of Obstetrics and Gynecology; Hokkaido University Graduate School of Medicine; Sapporo Japan
2. Women's Healthcare Center; Otaru General Hospital; Otaru Japan
3. Hokkaido Cancer Society; Sapporo Japan
4. Department of Women's Health Medicine; Faculty of Medicine; Hokkaido University; Sapporo Japan
5. Hokkaido Cancer Society; Asahikawa Japan
6. Department of Pathology; Sapporo Medical University; Sapporo Japan
7. Department of Surgical Pathology; Hokkaido University Hospital; Sapporo Japan
8. Department of Public Health; Faculty of Medicine; Hokkaido University; Sapporo Japan
9. Department of Obstetrics and Gynecology; Sapporo Medical University; Sapporo Japan
10. Department of Obstetrics and Gynecology; Asahikawa Medical University; Asahikawa Japan
11. Department of Obstetrics and Gynecology; Faculty of Medicine; Hokkaido University; Sapporo Japan