GDF6 and Ewing sarcoma: Although the data presented in this study suggest that GDF6 prodomain signaling, not GDF6 BMP signaling, plays a critical role in established Ewing sarcoma, it is possible that GDF6 gene expression results in coordinated regulation and crosstalk of GDF6 prodomain signaling and GDF6 BMP signaling in other biological context(s), which may include the initiation phase of Ewing sarcoma.