1. Swiss Childhood Cancer RegistryInstitute of Social and Preventive Medicine, University of Bern Bern Switzerland
2. Division of Pediatric Hematology and OncologyUniversity Children's Hospital Basel Basel Switzerland
3. Department for Epidemiology and Preventive MedicineMedicine Sociology, University of Regensburg Regensburg Germany
4. Division of Pediatric Hematology and OncologyUniversity Children's Hospital Bern Switzerland