1. Division of Pediatric Oncology/Hematology, Department of Pediatrics, Beatrix Children's Hospital, University Medical Center Groningen, University of Groningen, Groningen;
2. Department of Hematology, Erasmus University Medical Center, Rotterdam;
3. Department of Epidemiology, University Medical Center Groningen, University of Groningen, Groningen;
4. Department of Pediatric Oncology/Hematology, Erasmus MC–Sophia Children's Hospital, Rotterdam;
5. Division of Pediatric Oncology/Hematology, VU University Medical Center, Amsterdam; and
6. Dutch Childhood Oncology Group, The Hague, The Netherlands