Single cell RNA sequencing of Ewing sarcoma tumors demonstrate transcriptional heterogeneity and clonal evolution

Ewing sarcoma (ES) is the second most common bone cancer in children, accounting for 2% of pediatric cancer diagnoses. Patients who present with metastatic disease at the time of diagnosis have a dismal prognosis, compared to the >70% 5-year survival of those with localized disease. Here, we utilized single-cell RNA sequencing (scRNA-seq) to characterize the transcriptional landscape of primary ES tumors and surrounding tumor microenvironment (TME). Copy-number analysis identified subclonal evolution within patients even prior to treatment. Primary tumor samples demonstrate a heterogenous transcriptional landscape with several conserved gene expression programs composed of gene related to proliferation and EWS targets. We also were able to identify the composition of the tumor microenvironment and molecularly dissect the transcriptional profile of circulating tumor cells (CTCs) in peripheral blood at the time of diagnosis.