EWSR1 and Ewing sarcoma: The majority of Ewing's sarcoma and primitive neuroectodermal tumours are associated with a t(11;22)(q24;q12) chromosomal translocation, which results in the production of an EWS/FLI-1 fusion protein that comprises the amino terminus of the EWS gene and the carboxyl terminus of the FLI-1 gene.