1. a The Children's Hospital of Philadelphia, Division of Oncology, Philadelphia, Pennsylvania, USA;
2. f National Cancer Institute, Center for Cancer Research, Bethesda, Maryland, USA
3. b MD Anderson Cancer Center, Houston, Texas, USA;
4. c University of Michigan, Ann Arbor, Michigan, USA;
5. d Sarcoma Oncology Center, Los Angeles, California, USA;
6. e Massachusetts General Hospital, Boston, Massachusetts, USA;