Similar to other cancers, chemotherapy yielded a source of PtdSer as treatment with SN-38 (Fig. 4b and Supplementary Fig. 6a, b), etoposide (Fig. 4c and Supplementary Fig. 6c), or doxorubicin (Supplementary Fig. 6d, e) led to Ewing sarcoma cell apoptosis as demonstrated by increased cleaved-PARP and cleaved-caspase 3, which could be prevented by Z-VAD-FMK (a pan caspase inhibitor, Fig. 4d). Here, CASP3 is linked to Ewing sarcoma.