1. Department of Pediatric Oncology/Hematology, Children's Hospital of the City of Cologne, Amsterdamer Str. 59, 50735 Cologne, Germany
2. Department of Pediatric Oncology/Hematology, University Medical Center Charité, Campus Virchow, Augustenburger Pl. 1, 13353 Berlin, Germany
3. Department of Chemistry, University of Cologne, Greinstrasse 4, 50939 Cologne, Germany
4. Department of Pediatric Hematology/Oncology, Helios Clinic Schwerin, 19055 Schwerin, Germany
5. MSH Medical School Hamburg, Am Kaiserkai 1, 20457 Hamburg, Germany