Osteosarcoma in Children

The goal of this study is to learn whether children, adolescents, and young adults with newly diagnosed high-grade osteosarcoma can be safely discharged from the hospital at slightly higher methotrexate blood levels after receiving standard high-dose methotrexate chemotherapy. Participants are 22 years old or younger and are receiving standard MAP (high-dose methotrexate with doxorubicin and cisplatin) chemotherapy as part of their routine cancer treatment. The main questions this study aims to answer are: * Is hospital discharge at higher methotrexate levels safe, based on side effects or hospital re-admission within 7 days? * Can patient-derived osteosarcoma tumor organoids be successfully generated across multiple centers? Researchers will compare safety outcomes and hospital length of stay to historical patient data discharged at lower methotrexate levels. Participants will receive standard chemotherapy, meet study-defined discharge criteria, be monitored for side effects, and have the option to provide tumor and blood samples for future research.

The goal of this clinical trial is to define the maximum tolerated dose (MTD) and/or Recommended phase 2 dose (RP2D) of Tegavivint in combination with Gemcitabine in patients with relapsed or refractory osteosarcoma (OS). The study will also investigate the toxicities of Tegavivint in combination with gemcitabine in patients with relapsed or refractory OS.

The current study is to assess the prognostic value of Krüppel-like factors 4 and 7 in bone tumors, and its role in the disease progression.

This is an open-label, unicentric, single-arm Phase 2 pilot study to serve as a proof-of-concept of OMO-103 safety and activity in patients with advanced high-grade osteosarcoma. Patients will be treated at the RP2D (6.5 mg/kg as a weekly IV infusion) of OMO-103 to estimate anti-tumour activity and further characterise the safety, tolerability, PK, and PD of OMO-103 in advanced high-grade osteosarcoma patients. Ten (10) evaluable patients will be enrolled. At least 30% of patients will be \<18 years old. The first three patients 12-15 years of age will undergo additional safety monitoring. Patients will be treated until progression by RECIST v1.1 or intolerable toxicity.