While it was once believed that EWS-FLI1 was specific to Ewing's sarcoma, it is now known that EWS-FLI1 and related EWS-ETS fusions occur sporadically in other malignancies, including leukemias [83–87] and biphenotypic tumors, which have features of both myogenic and neuroectodermal differentiation [88]. This evidence concerns the gene EWSR1 and Ewing sarcoma.