HSV G207 in Children With Recurrent or Refractory Cerebellar Brain Tumors

This trial is testing an experimental treatment using a modified herpes virus (G207) injected directly into brain tumors in the cerebellum (back of the brain) in children and young adults whose cancer has come back or stopped responding to standard treatment. **You may be eligible if...** - You are between 3 and 21 years old - You have a confirmed malignant cerebellar brain tumor (such as medulloblastoma, glioblastoma, ependymoma, or other aggressive tumors) that has progressed or returned after standard treatment - Your tumor is between 1.0 and 3.0 cm and can be safely reached by surgery - You have recovered from prior treatments **You may NOT be eligible if...** - Your tumor cannot be safely reached by surgery - You have not yet received standard treatments (surgery, radiation, and/or chemotherapy) - You have active serious infections or other conditions that increase risk Talk to your doctor to see if this trial is right for you.