Hypofractionated Radiation in Combination With B7-H3-CAR T Cells for Pediatric Patients With Relapsed/Refractory Sarcomas

This study is testing a new treatment for children and young adults with bone and soft tissue cancers (sarcomas) that have come back or stopped responding to standard treatment. It combines targeted immune cells called CAR T cells — specially engineered to attack a protein found on these tumors — with a focused radiation treatment to help the immune cells work better. **You may be eligible if...** - You are 21 years old or younger - You have been diagnosed with osteosarcoma, Ewing sarcoma, rhabdomyosarcoma, or another soft tissue sarcoma - Your tumor tests positive for a protein called B7-H3 - Your cancer has come back or is not responding to standard first-line treatment - You are well enough to carry out some daily activities (performance score of 60 or above) - Your heart, kidneys, lungs, and liver are working adequately **You may NOT be eligible if...** - You have cancer that has spread to the brain or spinal cord - You have HIV or a serious immune system deficiency - You have an active, severe infection that is not controlled - You have another active cancer besides the sarcoma being treated - Your disease is progressing very rapidly Talk to your doctor to see if this trial is right for you.