Soluble B7-H3 as a Biomarker for Osteosarcoma

This study is looking at whether a protein called B7-H3, found in the blood, can be used as a marker to track osteosarcoma — a type of bone cancer — during chemotherapy treatment. Researchers want to see if blood levels of this protein change as patients respond to treatment. **You may be eligible if...** - You have been diagnosed with high-grade osteosarcoma (confirmed by a tissue biopsy) - You have not yet started any systemic (whole-body) cancer treatment - You are well enough to tolerate standard chemotherapy (ECOG performance score 0 or 1) - All your imaging and X-rays have been completed **You may NOT be eligible if...** - You cannot tolerate having blood drawn - Your medical records are not complete in the hospital's system - You are unable to tolerate the standard chemotherapy protocol used in this study - The study team determines you are otherwise unsuitable Talk to your doctor to see if this trial is right for you.