Study of MEK162 for Children With Low-Grade Gliomas

Patients with recurrent or progressive disease, as defined in the following three strata below, will be eligible. For eligibility determination, tumor imaging from at least two time-points must be available to document radiographic progression or recurrence. Patients with non-progressive refractory tumors will not be eligible. * Stratum 1: patients with LGG with a BRAF truncated fusion that is measurable in at least two dimensions on imaging. * Stratum 2: patients with NF1 and LGG that is measurable in at least two dimensions on imaging. * Stratum 3: Pediatric patients with a recurrent or progressive tumor thought to involve the Ras/Raf/ERK pathway but not included in strata 1 or 2 that is measurable in at least two dimensions on imaging. This includes any LGG not included in strata 1 or 2 (i.e., any LGG without a BRAF truncated fusion in a patient without NF1), any tumor other than LGG in a patient with NF1, and any other tumor with a documented activating BRAF, NRAS, or KRAS mutation. * Stratum 4 (surgical arm, target validation): Patients who meet criteria for stratum 1, 2, or 3 for whom tumor biopsy and/or resection is clinically indicated. * Tumor tissue for correlative studies must be available for all patients except those with NF1 and LGG (stratum 2) or any patient with optic pathway glioma (stratum 2 or 3), for whom tumor tissue is optional. * Patients must have received at least one prior chemotherapy or radiation regimen prior to progression. * At the time of enrollment, at least 6 weeks must have elapsed since the last dose of any nitrosourea, and the longer of 2 weeks or 3 half-lives must have elapsed since the last dose of any other tumor-directed medication. or biologic therapy. * At least 3 months must have elapsed since the last dose of irradiation to the target tumor(s) at the time of enrollment. * Patients must be \>1 year and \<18 years old. * Performance Score using the Karnofsky Performance Scale (patients \> 12 years old) or Lansky Play - Performance Scale (patients ≤ 12 years old) must be ≥ 60 assessed within two weeks prior to enrollment. * Participants must have normal organ and marrow function as defined below within two weeks prior to enrollment: * Absolute neutrophil count \> 1,000/mcL * Platelets \> 75,000/mcL and \> 7 days since last platelet transfusion. Hemoglobin \> 9 gm/dL and \> 7 days since last red blood cell transfusion * Not refractory to red cell or platelet transfusions * Hepatic: Total bilirubin ≤ 1.5 times the upper limit of normal; SGPT (ALT) and SGOT (AST) \< 3 times the institutional upper limit of normal * Renal: Serum creatinine which is less than 1.5 time the upper limit of institutional normal for age or GFR \> 70 ml/min/1.73m2 * QTc interval \< 450ms * Left ventricular ejection fraction (LVEF) \> 50% as determined by an echocardiogram * Female patients of childbearing potential must have negative serum or urine pregnancy test within 72 hours of the first dose of MEK162. Patient must not be pregnant or breast-feeding. Patients of childbearing or child-fathering potential must be willing to use a medically acceptable form of birth control, which includes abstinence, while being treated on this study and for 30 days following cessation of treatment. * Patient must be able to take oral/enteral medication. * Patient, parent, or legal guardian must be able to understand and willing to provide informed consent. * Patients must have recovered from the effects of prior therapy. Exclusion Criteria Patients with any of the following characteristics will not be eligible: * Patients for whom other curative or established standard-of-care therapeutic options with acceptable morbidity exist. * Patients with any significant medical illnesses that in the investigator's opinion cannot be adequately controlled with appropriate therapy or would compromise the patient's ability to tolerate this therapy. * History of Gilbert's syndrome * Patients receiving any other anticancer or experimental drug therapy. * Use of hematopoietic growth factors within 2 weeks prior to initiation of therapy. * Any other investigational agents within 2 weeks or ≤ 3 half-lives (whichever is longer) before start of study therapy. * Patients who have undergone surgery ≤ 3 weeks or who have not recovered from side effects of this procedure prior to receiving study drug. * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, impaired gastrointestinal function, or psychiatric illness/social situations that would limit compliance with study requirements. * History or current evidence of retinal vein occlusion (RVO) or predisposing factors to RVO (e.g. uncontrolled glaucoma or ocular hypertension, history of hyperviscosity or hypercoagulability syndromes). * History of retinal degenerative disease * Prior therapy with a MEK inhibitor * Impairment of gastrointestinal function (e.g., active ulcerative disease, uncontrolled nausea, vomiting, diarrhea, malabsorption syndrome) * Patients who have a neuromuscular disorder that is associated with elevated CK (e.g., inflammatory myopathies, muscular dystrophy, amyotrophic lateral sclerosis, spinal muscular atrophy). * Patients with uncontrolled hypertension Inclusion of Women, Minorities, and Other Underrepresented Populations This protocol is open to males and females of all races. See Inclusion Criteria above regarding specific eligibility requirements for female and male patients of child-bearing or child-fathering potential, respectively.