RecruitingEarly Phase 1Drug trialA Trial to Evaluate CSF ctDNA and Safety of Plixorafenib Alone or With Retifanlimab in Patients With BRAF-altered GliomaThe investigators will evaluate the sensitivity of ctDNA from plasma and CSF at baseline (defined as C1D1) and over time in response to treatment with plixorafenib alone or in combination with retifanlimab in patients with BRAF-V600E mutant glioma refractory to prior therapies.