Primary Objective:~1. To evaluate the ability of ulixertinib to penetrate the BBB in patients with recurrent MAPK-activated LGG (ulixertinib tumor concentration, tumor/plasma ratio and tumor/cerebrospinal fluid (CSF) ratio)~Secondary Objectives:~To assess anti-tumor activity of ulixertinib for patients with recurrent lower grade~MAPK-activated gliomas after surgical resection based on:~Median progression-free-survival (mPFS)~Objective response rate (ORR) at 12 months~Disease control rate (DCR) at 12 months~Duration of response (DOR)~Time to response (TTR)~Time to next intervention~To assess safety and tolerability of ulixertinib in MAPK-activated LGG
To learn if the study drug, ulixertinib, can cross over the blood-brain barrier in patients with recurrent brain tumors