Thus, methylseleninic acid, a drug reported to induce elevated expression of FoxO1 in ES cells, apoptosis of ES cells, and significant reduction of tumor growth in an orthotopic mouse xenotransplantation model, may be a potential target drug for Ewing sarcoma (Cidre-Aranaz and Alonso, 2015). Here, FOXO1 is linked to Ewing sarcoma.