1. Department of Gastroenterological Surgery, Stavanger University Hospital, Stavanger, Norway
2. Department of Surgical Sciences, University of Bergen, Bergen, Norway
3. Department of Medicine, Telemark Hospital, Skien, Norway
4. Department of Faculty of Medicine, University of Oslo, Norway
5. Department of Cancer Registry of Norway, Oslo, Norway
6. Department of Mathematics and Natural Sciences, University of Stavanger, Stavanger, Norway
7. Department of Medicine, Stavanger University Hospital, Stavanger, Norway