[1] Aarhus Univ Hosp, Dept Pediat, DK-8200 Aarhus N, Denmark
[2] Danish Canc Soc, Res Ctr, Copenhagen, Denmark
[3] Landspitali Univ Hosp, Childrens Hosp Iceland, Reykjavik, Iceland
[4] Lund Univ, Dept Clin Sci, Canc Epidemiol, Lund, Sweden
[5] Finnish Canc Registry, FIN-00170 Helsinki, Finland
[6] Jorvi Cent Hosp, Dept Pediat, Espoo, Finland
[7] Univ Iceland, Fac Med, Reykjavik, Iceland
[8] Iceland Canc Registry, Reykjavik, Iceland
[9] Norwegian Canc Registry, Oslo, Norway
[10] Lund Univ, Skane Univ Hosp, Dept Clin Sci Pediat Oncol & Hematol, Lund, Sweden