EWSR1 and Ewing sarcoma: A number of STSs are dependent from fusion proteins that act as or in complexes with transcription factors (TFs) such as the afore-mentioned PAX3-FOXO1 in RMS, EWS-FLI1 in Ewing sarcomas (ES), an STS that affects also bones, and SS18-SSX in synovial sarcomas (SS) (Riggi et al., 2014; Gryder et al., 2017; McBride et al., 2018).