Efficacy and Safety of Selumetinib in Adults With NF1 Who Have Symptomatic, Inoperable Plexiform Neurofibromas

Key Inclusion Criteria: * Adults ≥ 18 years at enrollment with diagnosis of NF1 with symptomatic, inoperable PN * At least one inoperable target PN measurable by volumetric MRI analysis * Chronic target PN pain score documented for minimum period during screening period * Stable chronic PN pain medication use at enrollment * Adequate organ and marrow function Key Exclusion Criteria: * Confirmed or suspected malignant glioma or MPNST (low grade glioma, including optic glioma not requiring systemic therapy or radiation therapy are exempt from this exclusion) * History of malignancy except for malignancy treated with curative intent with no known active disease ≥ 5 years before the first dose of study intervention and of low potential risk for recurrence * Clinically significant cardiovascular disease, including inherited coronary disease, acute coronary syndrome within 6 months prior to enrollment, uncontrolled angina, symptomatic heart failure, cardiomyopathy, severe valvular heart disease, abnormal LVEF and uncontrolled hypertension * Ophthalmological findings/conditions including intraocular pressure \> 21 mmHg, RPED/CSR or RVO * Prior exposure to MEK inhibitors