Dabrafenib and Trametinib for BRAF V600 Mutant Low-Grade Gliomas

Inclusion Criteria: * Participants must have histologically confirmed LGG World Health Organization (WHO) Grade I or II with BRAF V600 mutation confirmed by immunohistochemistry or sequencing * Participants must have measurable tumor. \* For participants with measurable disease, this will be defined as lesions that can be accurately measured in two dimensions (longest diameter to be recorded) with a minimum size of no less than double the slice thickness. Previously irradiated lesions are considered non-measurable except in cases of documented progression of the lesion since the completion of radiation therapy. Participants without measurable disease may be considered for enrollment and followed for survival and progression purposes but will not be included as part of a measurable disease cohort. * Cohort 1: * Participants must have no prior therapy, except for surgical intervention (i.e. biopsy or resection) * Participants may currently be taking dabrafenib and trametinib as frontline therapy, with a maximum duration of 21 months and participants must not yet have met criteria for confirmed best response as defined in this protocol. For participants entering the trial currently taking dabrafenib and trametinib, they must be taking a dose that is within 20% of the standard dosing for both drugs based on age and weight. Participants who are already on dabrafenib and trametinib when enrolling on trial and whose dosing deviates more than 20% from the protocol nomogram n…