In this **Phase 1/1b clinical trial**, researchers are studying the combination of two drugs, **Losartan** and **Sunitinib**, for treating **osteosarcoma**, a type of bone cancer. The goal is to find the highest dose that patients can handle without severe side effects. Initially, a small group will receive increasing doses to determine the safest level. Afterward, another group will receive this dose to check its effectiveness. **Key Points**: - **Duration & Visits**: The study involves multiple visits for dose adjustments and assessments. - **Eligibility**: Participants must be at least 10 years old, with confirmed osteosarcoma that has worsened after previous treatments. Patients must meet specific health criteria. - **Risks & Benefits**: Potential side effects from the drug combination; however, it may help manage osteosarcoma when other treatments haven't worked. Inclusion requires the ability to take oral medication and adequate function in organs like the heart and kidneys. Certain conditions like recent surgeries or uncontrolled bleeding disqualify participation. Participants agree to follow study procedures and not use other experimental drugs during the trial.