-  INCLUSION CRITERIA:

               1. Histological diagnosis

                  --Pathologically confirmed glioblastoma or gliosarcoma

               2. Patients must be eligible for definitive external beam radiotherapy and
                  temozolomide.

               3. Age >18 years. Because no dosing or adverse event data are currently available on
                  the use of Selinexor in combination with Temodar in patients <18 years of age,
                  children are excluded from this study.

               4. Patients should have a KPS greater than or equal to 70

               5. Absolute neutrophil count (ANC) >1.5x10^9/L; platelet count >100x10^9/L; and
                  hemoglobin (Hb) >9.0 g/dL within 7 days prior to enrollment. Note: the use of
                  transfusion or other intervention prior to cycle 1 day 1 to achieve Hb >9.0 g/dL
                  is acceptable.

               6. Ability of subject or Legally Authorized Representative (LAR) to understand and
                  the willingness to sign a written informed consent document.

               7. The effects of Selinexor on the developing human fetus are unknown. For this
                  reason and because Selinexor agents as well as other therapeutic agents used in
                  this trial are known to be teratogenic, women of child-bearing potential and men
                  must agree to use

                  adequate contraception (hormonal or barrier method of birth control; abstinence)
                  prior to study entry, for the duration of study treatment and for one month after
                  treatment. Should a woman become pregnant or suspect she is pregnant while she or
                  her partner is participating in this study, she should inform her treating
                  physician immediately.

               8. Patients must have had surgery and/or biopsy not greater than 8 weeks prior to
                  initial evaluation to be eligible for this study.

        EXCLUSION CRITERIA:

          1. Patients who are receiving any other investigational agents and have had prior therapy
             including:

               -  Patients who have previously received radiation therapy (RT) to the brain.

               -  Patients who received chemotherapy for the treatment of their glioma

               -  Patients who are being treated with implanted gliadel wafers

               -  Patients who are being treated with tumor treating fields

          2. History of allergic reactions attributed to compounds of similar chemical or biologic
             composition to selinexor or temozolomide used in study.

          3. Patients with coagulation problems and medically significant bleeding in the month
             prior to start of treatment (peptic ulcers, epistaxis, spontaneous bleeding). Prior
             history of DVT or PE is not exclusionary

          4. Patients with active uncontrolled or suspected infections

          5. Patients with severe liver dysfunction defined as:

               -  Total bilirubin greater than or equal to 1.5 x upper limit of normal (ULN)

               -  Serum glutamate pyruvate transaminase (SGPT) or called as Alanine

             aminotransferase (ALT) greater than or equal to 3 x ULN = 135 U/L; for the purpose of
             this study, the ULN for SGPT is 45 U/L

               -  Serum glutamic oxaloacetic transaminase (SGOT) or called as Aspartate
                  aminotransferase (AST) greater than or equal to 3 x ULN = 150 U/L; for the
                  purpose of this study, the ULN for SGOT is 50 U/L

               -  Serum albumin less than or equal to 2 x ULN

          6. Known active hepatitis A, B, or C infection

          7. HIV patients are not eligible because of their immunocompromised status and overlap of
             side effects between HAART therapy and radiation therapy.

          8. Patients must not have significantly diseased or obstructed gastrointestinal tract
             malabsorption, uncontrolled vomiting or diarrhea, or inability to swallow oral
             medication

          9. Pregnant women are excluded from this study because Selinexor could have the potential
             for teratogenic or abortifacient effects. Because there is an unknown but potential
             risk for adverse events in nursing infants secondary to treatment of the mother with
             Selinexor, breastfeeding should be discontinued if the mother is treated with
             Selinexor. These potential risks may also apply to temozolomide used in this study.

         10. Patients with pre-existing known or suspected radiation sensitivity syndromes will be
             excluded due to potential confounding effect on outcome.