EWSR1 and Ewing sarcoma: A673 Ewing sarcoma cells harbor EWS/FLI‐1 rearrangements, which are found in ≈90% of all Ewing sarcoma tumors.[18] Since the EWS/FLI‐1 rearrangements are absent in healthy donor's plasma, A673 cell‐derived EVs can be specifically quantified by detecting EWS/FLI‐1 mRNA using RT‐dPCR.