Ewing sarcoma is characterised by hallmarktranslocation events (most commonly EWSR1/FLI1).Prior studies have evaluated the prognostic impact of fusion transcript detection inthe peripheral blood or bone marrow using reverse transcription-polymerase chainreaction, yet have not shown consistent prognostic value.8,9 Likewise, measures of Ewing sarcoma tumour cells inthe peripheral blood and bone marrow by flow cytometry were notprognostic.9–11 A range of circulating biomarkers have beenevaluated in osteosarcoma, though none yet validated.12–15. Here, EWSR1 is linked to osteosarcoma.