Many cancers, such as osteosarcoma, neuroblastoma, and MRT/ATRT can be difficult to treat if they return after standard therapy. This clinical trial is testing a drug called panobinostat to see if it can help keep these tumours under control. Panobinostat is a type of “epigenetic” therapy, meaning it works by flipping “switches” inside cancer cells to slow down their growth. In this study, children and young adults receive a low daily dose of panobinostat as a pill for up to one year. The researchers are looking for the “sweet spot”: a dose that is strong enough to fight the cancer but gentle enough to minimise side effects. The team aims to find a new way to provide long term stability for patients with returning tumours.