1. Department of Gastroenterological Surgery Osaka University Hospital Suita Japan
2. Department of Gastroenterological Surgery Osaka International Cancer Institute Suita Japan
3. The Clinical Study Group of Osaka University Hepato‐Biliary‐Pancreatic Group Osaka Japan
4. Department of Surgery Kansai Rosai Hospital Amagasaki Japan
5. Department of Gastroenterological Surgery Kindai University Nara Hospital Ikoma Japan
6. Department of Surgery Toyonaka Municipal Hospital Toyonaka Japan
7. Department of Surgery Osaka Police Hospital Osaka Japan
8. Department of Gastroenterological Surgery Higashiosaka City Medical Center Higashiosaka Japan
9. Department of Surgery Osaka Rosai Hospital Sakai Japan
10. Department of Biomedical Statistics and Bioinformatics University Graduate School of Medicine Tyoto Japan