EWSR1 and neuroblastoma: Other liquid biopsy approaches have been developed including serial detection of hypermethylated DNA targets [38], exosomal microRNA (miRNA) [39] and, recently, characterisation of the cell-free DNA (cfDNA) in NB and EWS using targeted and untargeted approaches such as droplet digital PCR (ddPCR) and WGS has shown the ability to monitor tumour evolution based on genetic and epigenetic profiles [40, 41].