It has been shown that class 1 HDACs play a role in ES pathogenesis and that HDAC2 is overexpressed in ES patient samples, which suggests that, although pan-HDAC inhibitors may also be effective, specific class 1 HDAC inhibitors, such as romidepsin, may be a more specific approach to target ES cells. This evidence concerns the gene HDAC9 and Ewing sarcoma.