The goal of this study is to find out if DAY101 is safe, well-tolerated and how well it works compared to Standard of Care (SoC) chemotherapy in treating children, adolescent, and young adult patients under 25 years old with LGG with RAF alteration requiring frontline systemic therapy. Patients who join this study will be assigned by chance (like the flip of a coin, 50-50 chance) to receive either DAY101 or SoC chemotherapy.

Treatment will be given in cycles. For DAY101, the cycles have a duration of 4 weeks (28 days).. For SoC chemotherapy, the cycles are specific to the SoC chemotherapy regimen the patient will receive and are 4 to 6 weeks long. Treatment in the study may be continued as long as the tumor does not grow or the patient does not have side effects which cannot be tolerated. Total duration of treatment with DAY101 might last up to 5 years. SoC treatment is expected to last 1-1,5 years. Patients will be followed up after treatment termination until end of study participation, which is up to 5 years.