In particular, as MDM4 amplification is a characteristic of both Ewing and osteosarcoma, this study has examined the biological effects of XI-006 both as a single agent and in combination with standard chemotherapeutic agents and olaparib (PARP inhibitor) in a comprehensive panel of Ewing and osteosarcoma cell lines in vitro. This evidence concerns the gene MDM4 and osteosarcoma.