1 Childhood Cancer Research Group, Danish Cancer Institute, Copenhagen, Denmark.
2 Childhood Cancer Center, Skåne University Hospital, Lund, Sweden.
3 Department of Clinical Sciences, Lund University, Lund, Sweden.
4 University of Helsinki and Hospital for Children and Adolescents, Helsinki, Finland.
5 Norwegian Cancer Registry and Department of Pediatric Medicine, Oslo University Hospital and Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.
6 Department of Pediatrics, Aarhus University Hospital, Aarhus, Denmark.
7 Department of Pediatrics and Adolescent Medicine, Copenhagen University Hospital, Copenhagen, Denmark.
8 Department of Clinical Medicine, Faculty of Health, Aarhus University and Aarhus University Hospital, Aarhus, Denmark.