1. Department of Gastroenterological Surgery II, Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido 060‑8638, Japan
2. Department of Cardiovascular and Thoracic Surgery, Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido 060‑8638, Japan
3. Department of Surgical Pathology, Hokkaido University Hospital, Sapporo, Hokkaido 060‑8648, Japan
4. Department of Thoracic Surgery, Sapporo Minami Sanjo Hospital, Sapporo, Hokkaido 060‑0063, Japan