Tegavivint With Gemcitabine in Patients With Relapsed or Refractory Osteosarcoma

This study is testing a combination of two drugs — tegavivint and gemcitabine — in children, teens, and young adults with osteosarcoma (a type of bone cancer) that has come back or has not responded to prior treatment. It aims to find the right dose and assess the treatment's safety and effectiveness. **You may be eligible if...** - You have a confirmed diagnosis of osteosarcoma that has relapsed or is refractory - You previously received front-line chemotherapy including at least 3 of these drugs: methotrexate, doxorubicin, cisplatin, and ifosfamide - Your heart, liver, kidney, and bone marrow function are adequate - Your performance status (ability to function) meets requirements - You have measurable or evaluable disease **You may NOT be eligible if...** - You have active brain involvement from osteosarcoma - You are pregnant or breastfeeding - You are currently taking another experimental drug or anti-cancer treatment - You have received tegavivint before - You have received bisphosphonates within 4 weeks or denosumab within 6 months of enrollment - You have a known metabolic bone disorder - You have significant low calcium that does not improve with supplements Talk to your doctor to see if this trial is right for you.