SJ901: Evaluation of Mirdametinib in Children, Adolescents, and Young Adults With Low-Grade Glioma

Inclusion Criteria: Screening Phase * Participants with histologically confirmed or suspected low-grade glioma, including neuronal and mixed neuronal-glial tumors * Participant must have adequate tumor tissue from primary and/or relapsed tumor for central pathology review * For Phase 1: Projected to be ≥ 2 years and \< 25 years at the time of study enrollment * Participant's body surface area (BSA) at time of study enrollment must fall within the range outlined in the protocol for the specific dose level under evaluation: * Phase 1: Dose Finding/Dose-escalation * For Phase 1 participant's BSA must fall within the range specified in the protocol for the specific dose level under evaluation. * Phase 2: All Cohorts: * For Phase 2 of the study the upper BSA restrictions will be removed. * Participant and/or guardian can understand and is willing to sign a written informed consent document according to institutional guidelines Exclusion Criteria: Screening Phase * Participants with known current retinal pathology that is consistent with or a precursor for central serous retinopathy, retinal vein occlusion (RVO), or neovascular macular degeneration * Participants with a known malabsorption syndrome or preexisting gastrointestinal conditions that may impair absorption of mirdametinib (e.g., gastric bypass, lap band, or other gastric procedures) * Participant with a known history of liver disease or known hepatic or biliary abnormalities (except for Gilbert's syndro…