Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 3.0-99.0,  Neoplasms, Nerve Tissue Neurofibromatosis 1 Heredodegenerative Disorders, Nervous System Peripheral Nervous System Diseases Age: greater than or equal to 3 years of age, BSA greater than or equal to 0.55 m^2, and able to swallow intact capsules Diagnosis: must have either a clinical diagnosis of NF1 or a germline NF1 mutation, or in patients without the NF1 syndrome, demonstrate an NF1 mutation in the GIST verified in a CLIA certified laboratory. In patients without the NF1 syndrome, confirmation of the NF1 mutation in the GIST is required for enrollment a) For a clinical diagnosis of NF1 patients must have at least two of the diagnostic for NF1 listed below Six or more cafe-au-lait macules (greater or equal to 0.5cm in prepubertal subjects or greater than or equal to 1.5 cm in post pubertal subjects) Freckling in axilla or groin A neurofibroma or plexiform neurofibroma 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  Patients with evidence of another malignancy or benign tumor requiring chemotherapy or radiation therapy are excluded; however, those patients with a plexiform neurofibroma requiring treatment will be eligible as selumetinib has documented activity in plexiform neurofibromas Patients with a diagnosis of NF1 and GIST who do not meet other may enroll on the NF1 Natural History Study, and will be followed on this study. Should they require therapy for GIST based on evidence of progression, they may then enroll on study Patients who are receiving any other investigational agents Prior therapy with selumetinib or another specific MEK inhibitor is not permitted History of allergic reactions attributed to compounds of similar chemical or biologic composition to selumetinib or other agents used in study Previous MEK, RAS, or RAF inhibitor use Patients who anticipate the need for surgical intervention within the first three cycles (3 months), as surgical intervention during the period of DLT evaluation may affect analysis of adherence and/or make the subject inevaluable Patients with known brain metastases should be excluded from this clinical trial because of their poor prognosis and because they often develop progressive neurologic dysfunction that would confound the evaluation of neurologic and other adverse events Patients with the following cardiac conditions are excluded Uncontrolled hypertension (Adults: blood pressure [BP] of greater than or equal to 150/95 despite medical support/management. Participants 18 years of age and younger should have a blood pressure less than or equal to 95th percentile for age, height and gender. Preexisting hypertension in adults should be controlled (either with pharmacological or nonpharmacological methods) at the time of enrollment.)