GDF6 and synovial sarcoma: Consistent with GDF6 being an EWS-FLI1 target, GDF6 is highly expressed in Ewing sarcoma tumors and cell lines compared with mesenchymal stem cells, rhabdomyosarcoma cells, osteosarcoma cells, synovial sarcoma cells, and epithelial cells, such as 293, 293T, HeLa, and HCT116 (Figure 1E).