The EWS/FLI1 gene is well known as the driver gene of Ewing's sarcoma. We designed a novel pbi-shRNA™ EWS/FLI1 Type 1 LPX which has demonstrated sufficient specificity, safety and efficacy in animal testing to justify Phase I testing. Clinical safety (no ≥ grade 3 product related toxic effect) and target specific activity has been observed with other bi-shRNA products involving 147 cancer patients (698 separate dose administrations) (BB-IND 14205; BB-IND 14938). Moreover, safety has been observed with IV delivery of pbi-shRNA™ EWS/FLI1 Type 1 LPX in murine and swine testing via multidose IV administration.