Patients must have a body surface area (BSA) of >= . m^ at the time of study enrollment Patients must have a body surface area (BSA) >= . m^ Patients must have a body surface area >= . m^ at the time of study enrollment if enrolling on dose levels -; patients must have a body surface area >= . m^ at the time of study enrollment if enrolling on dose level Body surface area (BSA) must be > . and < . m^ Patients with a body surface area < . m^ are not eligible Patients must have a body surface area >= . m^ Patients must have a body surface area >= . m^ at enrollment Patients must have a body surface area >= . m^ at enrollment Patients enrolled after the drug supply of the mg strength has been exhausted must have a body surface area >= . m^ at enrollment and follow the dosing nomogram Patients must have a body surface area >= . m^ at enrollment Patients accruing to dose level must have a body surface area >= . m^ at the time of study enrollment; patients accruing to dose level must have a body surface area >= . m^ at the time of study enrollment; patients accruing to dose level - must have a body surface area >= . m^ at the time of study enrollment Eligible patients have a body surface area >= . m^ AND be able to swallow whole tablets at the time of study enrollment Body surface area (BSA) >= . m^ Body surface area (BSA) ? . m Patients who will be receiving the tablet formulation must have a body surface area (BSA) >= . m^ (square meter) at baseline. Patients must have a body surface area >= . m^ at the time of study enrollment Arms C and D only: body surface area < . m. Patients must have a body surface area (BSA) of >= . m^ at time of study enrollment Patients must have a body surface area >= . m^ at enrollment Patients must have a body surface area (BSA) >= . m^ Body surface area (BSA) greater than . m^ Body surface area (BSA) >= . m^ Body surface area (BSA): Subjects must have a body surface area ? . m at the time of the study enrollment, unless enrolled in Part E Patients with a body surface area >. m. Body surface area > . Patients must have a body surface area >= . m^ at enrollment Patients must have a body surface area (BSA) of >= . m^ at the time of study enrollment Body surface Area (For Dose Level -): Patients must be ? . m at the time of study enrollment. For subjects between the ages of - years only, body surface area (BSA) must be >= . m^ Body surface area >= . m^ Patients must have a body surface area (BSA) of >= . m^ at the time of study enrollment Body surface area (for Parts A, B and C): \r\n* Patients must have a body surface area (BSA) of >= . m^ at the time of study enrollment Part C: Patients must have a body surface area (BSA) >= . m^ at the time of study enrollment Patients with a body surface area (BSA) =< . m^ are excluded Patients receiving the formulated capsules must have a body surface area (BSA) >= . m^ at the time of study enrollment Rash must cover less than % of body surface area (BSA) To ensure that no patient will receive a dose of selinexor > mg/m^, body surface area (BSA) calculated by Dubois method must be > . m^ Serum creatinine =< . x the institutional upper limits of normal or corrected creatinine clearance of >= mg/ml/hr/. m^ body surface area (BSA) Body surface area (BSA) greater than . m^ Body surface area (BSA) >= . m^ Body surface area >= .m^ on dosage levels b, , and of the original treatment design Body surface area < . m^ for all dosage levels in the modified treatment design Obtained within days prior to registration: Serum creatinine =< . x the institutional upper limits of normal or corrected creatinine clearance of >= mg/ml/hr/. m^ body surface area (BSA) Patients must have a body surface area (BSA) >= . m^ at the time of study enrollment Body surface area (BSA) >= . m^ Patients with a creatinine clearance < ml/min/. m^ body surface area Rash must cover less than % of body surface area (BSA) Body surface area (BSA) ? . m. Patients age - years are eligible only if they have a body surface area (BSA) >= . m^ or weigh >= kg PHASE II: >= and =< years; body surface area (BSA) >= . m^, and able to swallow whole capsules Patients must have a body surface area >= . m^ at the time of study enrollment In order to limit dose deviations due to rounding, patients must have a body surface area of at least . m^ All patients must have an accurate pre-op height and weight and BSA (body surface area) calculation for CO (cardiac output) monitoring on FloTrac Area to be irradiated representing -% of total body surface area (TBSA) BSA (Body Surface Area) of <. m. Body Surface Area (BSA) (m) of <. Subjects whose body surface area (BSA) would expose them to < % or > % of the target dose Body Surface Area < . m at baseline, calculated by the Dubois or Mosteller method.