1. German Childhood Cancer Registry, Institute for Medical Biostatistics, Epidemiology and Informatics (IMBEI), University Medical Centre Mainz, Mainz, Germany;
2. Faculty of Health and Medical Sciences, Departments of Biochemistry and Physiology, University of Surrey, Guildford, Surrey, United Kingdom;
3. Pediatric Hematology and Oncology, University Children's Hospital Muenster, Muenster, Germany; and
4. Institute for Medical Biostatistics, Epidemiology and Informatics (IMBEI), University Medical Centre Mainz, Mainz, Germany