1. Pediatric Oncology and Hematology, University Düsseldorf, Germany
2. Pediatric Hematology and Oncology, University Münster, Münster, Germany
3. Pediatric Hematology and Oncology, Ludwig-Maximilians-University Munich, Munich, Germany
4. Pediatric Hematology and Oncology, University of Bonn, Bonn, Germany
5. Clinic for Pediatrics, Municipal Hospital, Dortmund, Germany
6. Kiel Paediatric Tumor Registry, Dept. of Paediatric Pathology, University of Kiel, Kiel, Germany