1 Department of Pediatric Oncology, Emma Children's Hospital/Academic Medical Center, PO Box 22660, 1100 DD Amsterdam, The Netherlands.
2 Department of Epidemiology, The Netherlands Cancer Institute, PO Box 90203, 1066 CX Amsterdam, The Netherlands.
3 Department of Pediatric Oncology and Hematology, University of Groningen, University Medical Center Groningen, PO Box 30.001, 9700 RB Groningen, The Netherlands.