1. Danish Cancer Society Research Center, Childhood Cancer Research Group, Copenhagen, Denmark;
2. Rigshospitalet, Department of Pediatric and Adolescent Medicine, Copenhagen University Hospital, Copenhagen, Denmark;
3. Unit of Statistics and Pharmacoepidemiology, Danish Cancer Society Research Center, Copenhagen, Denmark;
4. Department of Pediatric and Adolescent Medicine, Aarhus University Hospital, Aarhus, Denmark;
5. Department of Clinical Sciences, Lund University, Lund, Sweden;
6. Division of Paediatric Oncology and Haematology, Skane University Hospital, Lund, Sweden;
7. The Icelandic Cancer Registry, Reykjavik, Iceland;
8. Faculty of Medicine, University of Iceland, Reykjavik, Iceland;
9. The Finnish Cancer Registry, Helsinki, Finland;
10. Pediatric Oncology, National University Hospital of Iceland, Reykjavik, Iceland;
11. University of Helsinki Hospital for Children and Adolescents, Helsinki, Finland;
12. Department of Clinical Medicine, Faculty of Health, Aarhus University and University Hospital, Aarhus, Denmark