EWSR1 and Ewing sarcoma: We found that blocking the 26S proteasome by MG132 significantly increased the protein abundance of EWS–FLI1, but not the wild‐type EWSR1, in two Ewing sarcoma cell lines (A673 and SK‐N‐MC) (Figure 1A,B and Figure S1A,B (Supporting Information)), demonstrating that EWS–FLI1 levels are regulated through protein stability.