1. Department of Pediatrics and Adolescent Medicine, Center of Pediatric Oncology, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark.
2. The University Hospitals' Centre for Health Research (UCSF), Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark.
3. Section of Social Medicine, The University Hospitals' Centre for Health Research (UCSF), University of Copenhagen, Copenhagen, Denmark.
4. University of Kansas School of Medicine, Kansas City, Kansas.