Inclusion Criteria:

          -  Patients must have a body surface area (BSA) >= 0.84 m^2

          -  Diagnosis:

               -  Part A: Patients with recurrent or refractory solid tumors, including lymphoma
                  and CNS tumors, are eligible; patients must have had histologic verification of
                  malignancy at original diagnosis or relapse except in patients with intrinsic
                  brain stem tumors, optic pathway gliomas, or patients with pineal tumors and
                  elevations of cerebrospinal fluid (CSF) or serum tumor markers including
                  alpha-fetoprotein or beta-human chorionic gonadotropin (HCG)

               -  Part B: Patients with recurrent or refractory high grade glioma (World Health
                  Organization [WHO] grade III/IV) including disseminated tumors (excluding diffuse
                  intrinsic pontine glioma [DIPG]), not requiring surgical resection; patients must
                  have had histologic verification of malignancy at original diagnosis or relapse

               -  Part C: Patients with recurrent or refractory high grade glioma (WHO grade
                  III/IV) and requiring surgical resection (excluding DIPG and disseminated
                  tumors), who in the opinion of treating physicians, are medically stable to
                  receive 2 doses of selinexor (8-10 days of treatment) before undergoing surgery
                  without compromising the success of the procedure; note that if, in the opinion
                  of treating physicians, current symptoms necessitate surgery before 2 doses will
                  be able to be received, surgery should not be delayed to administer selinexor,
                  and the patient would be ineligible for protocol therapy

          -  Disease status:

               -  Part A: Patients must have either measurable or evaluable disease

               -  Parts B and C: Patients must have measurable disease on imaging

          -  Patient's current disease state must be one for which there is no known curative
             therapy or therapy proven to prolong survival with an acceptable quality of life

          -  Karnofsky >= 50% for patients > 16 years of age and Lansky >= 50 for patients =< 16
             years of age; Note: Neurologic deficits in patients with CNS tumors must have been
             relatively stable for at least 7 days prior to study enrollment; patients who are
             unable to walk because of paralysis, but who are up in a wheelchair, will be
             considered ambulatory for the purpose of assessing the performance score

          -  Patients must have fully recovered from the acute toxic effects of all prior
             anti-cancer therapy and must meet the following minimum duration from prior
             anti-cancer directed therapy prior to enrollment; if after the required timeframe, the
             numerical eligibility criteria are met, e.g. blood count criteria, the patient is
             considered to have recovered adequately

               -  Myelosuppressive chemotherapy: At least 21 days after the last dose of
                  myelosuppressive chemotherapy (42 days if prior nitrosourea)

               -  Hematopoietic growth factors: At least 14 days after the last dose of a
                  long-acting growth factor (e.g. Neulasta) or 7 days for short-acting growth
                  factor; for agents that have known adverse events occurring beyond 7 days after
                  administration, this period must be extended beyond the time during which adverse
                  events are known to occur; the duration of this interval must be discussed with
                  the study chair

               -  Biologic (anti-neoplastic agent): At least 7 days after the last dose of a
                  biologic agent; for agents that have known adverse events occurring beyond 7 days
                  after administration, this period must be extended beyond the time during which
                  adverse events are known to occur; the duration of this interval must be
                  discussed with the study chair

               -  Immunotherapy: At least 42 days after the completion of any type of
                  immunotherapy, e.g. tumor vaccines

               -  Antibodies: >= 21 days must have elapsed from infusion of last dose of antibody,
                  and toxicity related to prior antibody therapy must be recovered to grade =< 1

               -  Corticosteroids: If used to modify immune adverse events related to prior
                  therapy, >= 14 days must have elapsed since last dose of corticosteroid

               -  External beam radiation therapy (XRT): At least 14 days after local palliative
                  XRT (small port); at least 150 days must have elapsed if prior total body
                  irradiation (TBI), craniospinal XRT or if >= 50% radiation of pelvis; at least 42
                  days must have elapsed if other substantial bone marrow (BM) radiation

               -  Stem cell infusion without TBI: No evidence of active graft vs. host disease and
                  at least 56 days must have elapsed after transplant or stem cell infusion

               -  Patients must not have received prior exposure to selinexor

          -  For patients with solid tumors without known bone marrow involvement:

          -  * Peripheral absolute neutrophil count (ANC) >= 1000/mm^3

          -  * Platelet count >= 100,000/mm^3 (transfusion independent, defined as not receiving
             platelet transfusions for at least 7 days prior to enrollment)

          -  * Hemoglobin >= 8.0 g/dL at baseline (may receive red blood cell [RBC] transfusions)

          -  Patients with known bone marrow metastatic disease will be eligible for study if they
             meet the blood counts (may receive transfusions provided they are not known to be
             refractory to red cell or platelet transfusions); these patients will not be evaluable
             for hematologic toxicity; at least 5 of every cohort of 6 patients must be evaluable
             for hematologic toxicity for the dose-escalation part of the study; if dose-limiting
             hematologic toxicity is observed, all subsequent patients enrolled on Part A must be
             evaluable for hematologic toxicity

          -  Creatinine clearance or radioisotope glomerular filtration rate (GFR) >= 70
             ml/min/1.73 m^2 or

          -  A serum creatinine based on age/gender as follows:

               -  =< 0.6 mg/dL (patients age 1 to < 2 years)

               -  =< 0.8 mg/dL (patients age 2 to < 6 years)

               -  =< 1 mg/dL (patients age 6 to < 10 years)

               -  =< 1.2 mg/dL (patients age 10 to < 13 years)

               -  =< 1.4 mg/dL (female patients age >= 13 years)

               -  =< 1.5 mg/dL (male patients age 13 to < 16 years)

               -  =< 1.7 mg/dL (male patients age >= 16 years)

          -  Total bilirubin =< 1.5 x upper limit of normal (ULN) for age

          -  Serum glutamate pyruvate transaminase (SGPT) (alanine aminotransferase [ALT]) =< 3 x
             ULN = 135 U/L; for the purpose of this study, the ULN for SGPT is 45 U/L

          -  Serum albumin >= 2 g/dL

          -  Serum amylase =< 1.5 x ULN

          -  Serum lipase =< 1.5 x ULN

          -  Patients with seizure disorder may be enrolled if on anticonvulsants and well
             controlled

          -  Patients must be able to swallow tablets whole

          -  Part C: Archived paraffin-embedded tissue (20 unstained slides or a tumor block) from
             a prior resection must be available as a control for correlative studies; if tissue
             blocks or slides are unavailable, the study chair must be notified prior to enrollment

          -  All patients and/or their parents or legally authorized representatives must sign a
             written informed consent; assent, when appropriate, will be obtained according to
             institutional guidelines

        Exclusion Criteria:

          -  Pregnant or breast-feeding women will not be entered on this study, since there is yet
             no available information regarding human fetal or teratogenic toxicities; based on its
             mechanism of action and findings in animals, selinexor may cause fetal harm when
             administered to a pregnant woman; pregnancy tests must be obtained in girls who are
             post-menarchal; males with female partners of reproductive potential or females of
             reproductive potential may not participate unless they have agreed to use two
             effective methods of birth control- including a medically accepted barrier method of
             contraceptive method (e.g., male or female condom) for the entire period in which they
             are receiving protocol therapy and for at least 1 week following their last dose of
             study drug; abstinence is an acceptable method of birth control

          -  Concomitant medications

               -  Corticosteroids: Patients receiving corticosteroids who have not been on a stable
                  or decreasing dose of corticosteroid for at least 7 days prior to enrollment are
                  not eligible; if used to modify immune adverse events related to prior therapy,
                  >= 14 days must have elapsed since last dose of corticosteroid

               -  Investigational drugs: Patients who are currently receiving another
                  investigational drug are not eligible

               -  Anti-cancer agents: Patients who are currently receiving other anti-cancer agents
                  are not eligible

          -  Patients who have an uncontrolled infection are not eligible

          -  Patients who have received a prior solid organ transplantation are not eligible

          -  Patients who, in the opinion of the investigator, may not be able to comply with the
             safety monitoring requirements of the study are not eligible

          -  Patients with body mass index (BMI) < 3rd percentile for age, as defined by WHO
             criteria for patients 1-2 years of age and Centers for Disease Control and Prevention
             (CDC) criteria for patients > 2 years of age, are not eligible

          -  Patients with grade 3 ataxia or grade >1 extrapyramidal movement disorder are not
             eligible

          -  Patients with known macular degeneration, uncontrolled glaucoma, or cataracts are not
             eligible