1. Childhood Cancer Research GroupDanish Cancer Society Research Center Copenhagen Denmark
2. Unit of EpidemiologyInstitute of Environmental Medicine, Karolinska Institutet Stockholm Sweden
3. Finnish Cancer Registry Helsinki Finland
4. Children's HospitalUniversity of Helsinki and Helsinki University Hospital Helsinki Finland
5. Department of PaediatricsAarhus University Hospital Aarhus Denmark
6. Department of Clinical MedicineFaculty of Health, Aarhus University Aarhus Denmark