Our current findings demonstrate that more spontaneous lung metastases develop at baseline when comparing orthotopic Ewing sarcoma tumors developed in hu-CD34+ mice versus NSG mice, suggesting that immune mechanisms contribute to Ewing sarcoma metastasis and that there may an advantage to utilizing our hu-CD34+ model in future studies specifically focused on Ewing sarcoma lung metastases. The gene discussed is CD34; the disease is Ewing sarcoma.