Liothyronine in Combination With BIT Regimen for Medulloblastoma With or Without Minimal Residual Disease

OUTLINE: This is an intra-patient dose escalation (Phase 1 (Cohort 1)) followed by a Phase 2 (Cohort 2) study. Cohort 1: Children and young adults with relapsed or progressive disease following standard upfront therapy (including craniospinal radiation or high dose chemotherapy with autologous stem cell rescue). evaluating the safety and efficacy of combination L-T3 with BIT. Cohort 2: Children and young adults with medulloblastoma and CSF cell-free deoxyribonucleic acid (cf-DNA) positivity without radiographic disease progression/recurrence following standard upfront therapy. This is a Phase 2 study to evaluate clearance of Circulating free DNA (cfDNA) positive disease in CSF in response to L-T3 monotherapy at the RP2D (established as part of Cohort 1; Phase 1) as single agent. Participants may continue therapy for up to 12 cycles if there is no evidence of unacceptable toxicity, disease progression, or withdrawal of consent. For participants that are benefiting from therapy, they may continue L-T3 monotherapy for one additional year (24 cycles total therapy). Treatment beyond that specified in the protocol should be discussed with the study chairs. Duration of Follow up Participants will enter follow up after the 30-day toxicity period. Follow-up procedures are to be captured under the Pediatric NeuroOncology Consortium (PNOC) COMP protocol with the exception of protocol defined follow up procedures. Participants will be followed under the PNOC COMP protocol until death or withdrawal from study. The study will complete enrollment within 5 years from the time the study opens to accrual (including 3 years for enrollment and 2 years of long term follow up).