1. Clinic for Pediatric Oncology, Hematology, and Clinical Immunology, Heinrich Heine University of Duesseldorf, Duesseldorf, Germany;
2. Clinic for Pediatric Hematology and Oncology, University Hospital, Hamburg-Eppendorf, Germany; and
3. Department of Pediatric Oncology/Hematology, Erasmus MC/Sophia Children's Hospital, Erasmus University Medical Center, Rotterdam, The Netherlands