1. Danish Cancer Society Research Center; Copenhagen Denmark
2. Department of Pediatrics; Aarhus University Hospital Skejby; Aarhus Denmark
3. The Icelandic Cancer Registry; Reykjavik Iceland
4. Faculty of Medicine, Laeknagardur, University of Iceland; Reykjavik Iceland
5. Department of Cancer Epidemiology; Lund University; Lund Sweden
6. Department of Pediatrics, Oslo University Hospital, Nydalen; Oslo Norway
7. Faculty of Medicine, University of Oslo, Blindern; Oslo Norway
8. The Norwegian Cancer Registry; Majorstuen Oslo Norway
9. Finnish Cancer Registry; Helsinki Finland