Fimepinostat in Treating Brain Tumors in Children and Young Adults

Inclusion Criteria: * Patients must have one of the following histologically confirmed diagnoses (histologic confirmation from initial diagnosis acceptable, as appropriate): * Stratum A: Newly diagnosed diffuse intrinsic pontine glioma (WHO grade II-IV) - this stratum does not require tissue confirmation at time of enrollment, but diagnostic confirmation will be required to continue on study after biopsy. Patients with newly diagnosed DIPG will be eligible to enroll before or after standard of care radiation, but must be eligible for a biopsy. Newly diagnosed DIPG stratum should not have received prior therapy before the initiation of fimepinostat, with the exception of those patients who received temozolomide during radiation therapy or who previously received radiation as per standard of care and have not yet undergone a biopsy. All patients who have received therapy other than radiation and temozolomide should be discussed with study chair(s) prior to enrollment. Patients enrolling after standard of care radiation must be enrolled within 14 weeks of completion of radiotherapy. * Stratum B: Recurrent medulloblastoma (WHO grade IV), any molecular subtype * Stratum C: Recurrent high-grade glioma (HGG), including anaplastic astrocytoma (WHO grade III) and glioblastoma (WHO grade IV) * Stratum B \& C: Patients in the recurrent medulloblastoma or recurrent HGG arm can have locally recurrent or disseminated disease, provided resection/biopsy would still be clinically…