EWSR1 and Ewing sarcoma: Sarcoma diagnosis relies, not only on morphological and immunohistochemical features, but also on molecular alterations, such as EWS/FLI1 fusion in Ewing sarcoma (EWS), SS18-SSX fusion in synovial sarcoma, or kit mutation in gastrointestinal stromal tumors (GIST) [1].