Grade 2 Astrocytoma or Oligodendroglioma With an IDH1 or IDH2 Mutation

The objective of this study is to evaluate the safety, tolerability, efficacy profile, and effect on growth and development of vorasidenib in pediatric participants aged 12 to \< 18 years old with grade 2 glioma with an IDH1 or IDH2 mutation. The study includes a screening period, a treatment period consisting of continuous 28-day cycles of treatment, a safety follow-up period and a long-term follow-up period. The long-term follow-up period will assess participants for growth, development, and long-term safety impacts for approximately 5 years after the start of treatment or until Tanner Stage V is reached (whichever is later). Participants may undergo blood tests, heart tests (electrocardiogram (ECG)), imaging (MRI, X-ray), vital sign checks, and physical exams.