EWSR1 and Ewing sarcoma: In this regard, endothelial, mesodermal, epithelial, neural, and mesenchymal cells have all been hypothesized as an origin, but there is substantial research indicating that mesenchymal stem cells (MSC) may be the original progenitor of Ewing tumor proliferation [9], and Ewing tumors most often harbor nonrandom balanced chromosomal translocations of the EWS gene on chromosome 22 and any one of several ETS family genes.