Observational Study in Localized Osteosarcoma

This observational study is following children and young adults with high-grade osteosarcoma (a type of bone cancer) of the arms or legs who are being treated with standard chemotherapy. The goal is to collect data to better understand how this cancer behaves and how different patients respond to treatment. **You may be eligible if...** - You are 40 years old or younger at the time of diagnosis - You have been diagnosed with high-grade osteosarcoma of the limbs (arms or legs) - Your disease is localized (has not spread to distant organs; skip metastases within the limb are okay) - You have adequate organ function to receive recommended chemotherapy - You (or your parents/guardian if you are a minor) have given written consent **You may NOT be eligible if...** - Your cancer has spread to distant parts of the body (metastases) - You have a different subtype of osteosarcoma (periosteal, parosteal, or secondary) - You have a medical condition that prevents you from receiving the recommended treatment Talk to your doctor to see if this trial is right for you.