Acknowledgement
The authors thank the Spanish Society of Pediatric Hemato-Oncology (SEHOP) for patient data management.
Declaration of interest
This work was supported by FIS [PI14/01008] and RTICC [RD12/0036/0020], grants from the ISCIII & FEDER (European Regional Development Fund), Spain. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.