We found that treatment with JS-K significantly reduced tumor growth (Figure 4C, ANOVA Test p = 0.023) and increased overall survival (Figure 4D, Mantel–Cox Test, p = 0.0002), strongly suggesting that this GSTM4 pro-drug has anti-tumorigenic effects that can be exploited for the treatment of Ewing sarcoma. Here, GSTM4 is linked to Ewing sarcoma.