a Princess M ´ axima Center for Pediatric Oncology, Utrecht, the Netherlands b Department of Pediatric Oncology, CHU Nantes, Nantes, France c Paediatric Oncology, Astrid Lindgren Children ' s Hospital, Karolinska University Hospital, Stockholm, Sweden, and Childhood Cancer Research Unit, Department of Women ' s and Children ' s Health, Karolinska Institutet, Stockholm, Sweden d Unit ´ e de M ´ ethodologie et Biostatistiques, Centre Oscar Lambret, Lille, France e Universit ´ e Paris-Saclay, Universit ´ e Paris-Sud, UVSQ, CESP, INSERM, U1018 ONCOSTAT, F-94085 Villejuif, France f Department of Medical Oncology, Cochin Hospital, Cochin Institute, INSERMU1016, Paris Cancer Institute, CARPEM, AP-HP, Paris, France g Department of Oncology, University College London Cancer Institute, London, UK h Osteoncology, Bone and Soft Tissue Sarcomas and Innovative Therapies, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy i Department of Oncology, Oslo University Hospital, Norway j St. Anna Children ' s Hospital, Department of Pediatrics, Medical University Vienna, Vienna, Austria k St. Anna Children ' s Cancer Research Institute (CCRI), Vienna, Austria l Klinikum Stuttgart-Olgahospital, Stuttgart, Germany m Department of Oncology for Child and Adolescents, Gustave Roussy Cancer Center, Paris-Saclay University, Villejuif, France n National Institute for Health and Medical Research (INSERM) U1015, BiiOSTeam, Gustave Roussy Institute, Villejuif, France