MEK 1/2 Inhibitor Selumetinib (AZD6244 Hydrogen Sulfate) in Adults With Neurofibromatosis Type 1 (NF1) and Inoperable Plexiform Neurofibromas

Background: Neurofibromatosis type 1 (NF1) is a disorder that can cause plexiform neurofibromas (PNs). These are tumors that grow along nerves. Some PNs cause serious health problems. PNs often can t be operated on because of their large size, location, or number. There are no effective treatments known for people with NF1 and PNs. Researchers want to test if the drug selumetinib (AZD6244 hydrogen sulfate) causes PNs to shrink or slows down their growth. Objectives: To test if selumetinib helps treat PNs. To test how the body handles selumetinib and how it affects peoples symptoms. Eligibility: People ages 18 and older with NF1, with an inoperable PN that causes morbidity or is growing Design: Participants will be screened with: Medical history and physical exam Blood, urine, and heart tests Eye exam MRI: They lie in a machine that takes pictures of the body. PN biopsy: A small piece of the tumor is removed by a large needle. Questionnaires Participants will swallow selumetinib capsules every 12 hours for several 28-day cycles. The capsules are taken with a full glass of water on an empty stomach. Participants may have only water for 2 hours before and 1 hour after each dose. Participants will keep a drug diary. They will continue taking the drug as long as they tolerate it and their disease doesn t progress. Participants will have several visits throughout the study. These will include repeats of the screening tests. Participants will have a final visit after they stop taking selumetinib.

* INCLUSION CRITERIA: * Patients must have positive genetic testing for NF1 in a CLIA certified laboratory or a diagnosis of NF1 based on clinical NIH consensus criteria of at least one other diagnostic criterion in addition to the presence of a PN. NF1 mutation analysis will be performed on germline DNA. Histologic confirmation of tumor is not necessary in the presence of consistent clinical and imaging findings, but should be considered if malignant transformation of a PN is clinically suspected. Additional criteria are as follows: * Six or more cafe-au-lait macules (\>=0.5cm in prepubertal subjects or \>=1.5 cm in post pubertal subjects) * Freckling in axilla or groin * Optic glioma * Two or more Lisch nodules * A distinctive bony lesion (dysplasia of the sphenoid bone or dysplasia or thinning of long bone cortex) * A first-degree relative with NF1 * Measurable disease: Patients must have at least one measurable PN, defined as a lesion of at least 3 cm measured in one dimension. Patients who underwent surgery for resection of a PN are eligible provided the PN was incompletely resected and is measurable as per criteria above. Measurability and suitability for volumetric MRI analysis of the target PN must be confirmed with the NCI POB prior to enrolling a patient. The target PN will be defined as the clinically most relevant PN, which has to be amenable to volumetric MRI analysis. PN will be classified as typical PN versus nodular PN versus solitary nodular PN prior to enrollment * The PN must be inoperable, defined as a PN that cannot be surgically completely removed without risk for substantial morbidity due to: encasement of or close proximity to vital structures, invasiveness, or high vascularity of the PN. The PN either causes morbidity or it is growing and has the potential to cause morbidity such as (but not limited to): Head and neck lesions that could compromise the airway or great vessels, paraspinal lesions that can cause myelopathy, brachial or lumbar plexus lesions that could cause nerve compression and loss of function, lesions that could result in major deformity (e.g., orbital lesions) or are significantly disfiguring, and lesions of the extremity that cause limb hypertrophy or loss of function or pain. PN growth will be defined as a \>=20% increase in PN volume within approximately 3 years prior to enrollment on this trial. * Patients must have a PN amenable to a percutaneous biopsy to participate in the biopsy portion of this study, and must be willing to undergo pre-, and on treatment tumor biopsies. There should be no contraindication for serial biopsies. NOTE: Up to 10 patients who meet all criteria, but have PN which cannot be biopsied safely, will be eligible for the treatment portion of the study. * Must be able to undergo serial MRI scans for response evaluation * Age \>=18 years * ECOG performance status \=10 g/dL (not requiring RBC transfusions) * Absolute neutrophil count \>=1,500/mcL * Platelets \>=100,000/mcL (not requiring platelet transfusions) * Total bilirubin \