Phase 1/2 Study of Mirdametinib + Vinblastine for Newly Diagnosed/Previously Untreated PLGG + Activation of MAPK

This is a 3-part open-label study (feasibility phase, treatment phase and follow-up phase) of orally administered mirdametinib in combination with intravenous vinblastine chemotherapy in patients with PLGG with activation of MAPK pathway. Feasibility Phase: The maximum tolerated/recommended phase 2 dose (MTD/RP2D) of the mirdametinib plus vinblastine combination will be assessed using a modified Rolling-6 design. Treatment Phase: Patients will receive mirdametinib twice daily (continuously) at a fixed dose (2mg/m2 po BID up to 4 mg BID) for a total of 13 cycles (28 days cycle). Weekly intravenous vinblastine at MTD will be given for a total of 17 cycles. If adverse events occur, two dose reductions are allowed. Follow-up Phase: Following the end of treatment, patients will be scheduled for a follow-up visit every 6 months for 36 months to evaluate PFS, TTP and OS.