Quantification of genomic EWSR1 fusion sequences from plasma of Ewing sarcoma (EwS) patients for therapy monitoring and relapse detection

Background: Cell free circulating tumor DNA (ctDNA) has been shown to represent a biomarker in several common cancers of adulthood, taking advantage of recurrent point-mutations. We evaluated the use of the causative genomic fusion sequence as non-invasive tumor marker in pediatric EwS. Method: Detectability and correlation of EWSR1-FLI1 copies with tumor burden were first explored in EwS xenograft mice. Subsequently, plasma samples from EwS patients were analyzed before and during chemotherapy using ddPCR. Results: Kinetics of EWSR1-FLI1 levels are correlated with the tumor burden. Most EwS patients showed a fa…