Plasma DNa-Based Molecular Diagnosis, Prognostication, and Monitoring of Patients With EWSR1 Fusion-Positive Sarcomas

Purpose Ewing sarcoma (ES) and desmoplastic small round cell tumors (DSRCTs) are aggressive sarcomas molecularly characterized by EWSR1 gene fusions. As pathognomonic genomic events in these respective tumor types, EWSR1 fusions represent robust potential biomarkers for disease monitoring. Methods To investigate the feasibility of identifying EWSR1 fusions in plasma-derived cell-free DNA (cfDNA) from patients with ES and DSRCT, we evaluated two complementary approaches in samples from 17 patients with radiographic evidence of disease. The first approach involved identification of patient-specific genomic EWSR1 fusion breakpoints in formalin-fixed, paraffin-embedded tumor DNA using a broad, hybridization capture-based next-generation sequencing (NGS) panel, followed by design of patient-specific droplet digital polymerase chain reaction (ddPCR) assays for plasma cfDNA interrogation. The second approach used a disease-tailored targeted hybridization capture-based NGS panel applied directly to cfDNA, which included EWSR1 as well as several other genes with potential prognostic use. Results EWSR1 fusions were identified in 11 of 11 (100%) ES and five of six (83%) DSRCT cfDNA samples by ddPCR, whereas 10 of 11 (91%) and four of six (67%) were identified by NGS. The ddPCR approach had higher sensitivity, ranging between 0.009% and 0.018%. However, the hybrid capturebased NGS assay identified the precise fusion breakpoints in the majority of cfDNA samples, as well as mutations in TP53 and STAG2, two other recurrent, clinically significant alterations in ES, all without prior knowledge of the tumor genotype. Conclusion These results provide a compelling rationale for an integrated approach using both NGS and ddPCR for plasma cfDNA-based biomarker evaluations in prospective cooperative group studies. Precis Oncol 00. (C) 2017 by American Society of Clinical Oncology