In in vitro assays, K‐234 inhibited the growth of Ewing's sarcomas with various fusion types, including A‐673 and TC‐71 with the type 1 fusion of EWS‐FLI1, SK‐ES‐1, and RE‐ES with the type 2 fusion, and MHH‐ES‐1 and CADO‐ES1 with EWS‐ERG (Figure 2A,B). This evidence concerns the gene ERG and Ewing sarcoma.