1 University College London Great Ormond Street Institute of Child Health, London, UK; Department of Paediatric Oncology and Haematology, Rigshospitalet, Copenhagen, Denmark. Electronic address: j.brok@ucl.ac.uk.
2 University College London Great Ormond Street Institute of Child Health, London, UK.
3 Department of Medical Oncology and Hematology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.