1. Swiss Childhood Cancer Registry, Institute of Social and Preventive Medicine; University of Bern; Bern Switzerland
2. Division of Pediatric Hematology/Oncology; University Children's Hospital Basel; Basel Switzerland
3. Department of Pediatric Oncology, University Children's Hospital Zurich; University of Zurich; Zurich Switzerland
4. Department of ENT, Head and Neck Surgery; University Hospital Bern; University of Bern; Bern Switzerland