Inclusion Criteria:

          1. Patients must have either of the following:

               1. Relapsed/refractory leukemia in 2nd or greater relapse or who have failed at
                  least one re-induction attempt after relapse or for refractory disease. Patients
                  must meet the WHO classification with ≥ 5% blasts in the bone marrow or must have
                  definitive extramedullary disease (e.g. chloromas, skin lesions). Patients may
                  have asymptomatic CNS 1 or CNS 2 disease, but not CNS 3 or symptomatic CNS
                  disease.

                  OR

               2. Relapsed/refractory non-CNS solid tumor that has not responded or has relapsed
                  and for which no standard treatment is available. Patients may not have primary
                  CNS tumors or CNS metastases. Lymphoma patients are permitted. Patients do not
                  need to have measurable disease.

          2. Age 6 months - 29.99 years at enrollment

          3. Life expectancy ≥ 3 months

          4. Lansky or Karnofsky ≥50

          5. Prior therapy

               1. Patient must have fully recovered from the acute toxic effects of all prior
                  chemotherapy, immunotherapy, radiotherapy, or surgery prior to study entry.

               2. Myelosuppressive therapy- At least 14 days must have elapsed since the
                  administration of previous therapy. Six weeks must have elapsed from the
                  administration of nitrosureas or mitomycin C. For patients with ALL on
                  maintenance therapy, they may be eligible if 7 days have elapsed and they are
                  recovered from the toxic effects of the chemotherapy. This restriction does not
                  include intrathecal chemotherapy, which is permitted.

               3. Biologic agents- At least 14 days must have elapsed since the completion of
                  therapy with a biologic agent such as a monoclonal antibody. Seven days must have
                  elapsed since the last dose of retinoids

               4. Radiation therapy - At least 14 days must have elapsed for local XRT. At least 90
                  days must have elapsed if prior radiation to ≥50% of the pelvis, the spine, or
                  other substantial bone marrow radiation including TBI.

               5. Hematopoietic growth factors- At least 7 days must have elapsed since the last
                  dose of G-CSF or GM-CSF. At least 14 days must have elapsed since last dose of
                  pegfilgrastim (Neulasta®).

          6. Patient must be ≥ 3 months from hematopoietic stem cell transplant, must not have
             active GVHD, and must be off all immunosuppression

          7. Organ function:

               1. Either a serum creatinine ≤ ULN for age, or calculated or measured GFR ≥ 70
                  mL/min/1.73 m2

               2. Total bilirubin ≤ 1.5 x ULN for age, direct bilirubin ≤ ULN for age

               3. AST and ALT ≤ 3 x ULN for age unless elevation can be clearly attributed to liver
                  leukemia or metastases

               4. ECHO shortening fraction ≥ 27%

               5. Pulse Oximetry measurement ≥ 95% saturation without supplemental oxygen

          8. Bone marrow function:

               1. Hgb ≥10 g/dL - can be transfused

               2. Plts ≥ 75,000 - cannot be transfused (must be ≥ 7 days from last plt transfusion)

               3. ANC ≥ 750 - cannot be transfused (must be ≥ 72 hours from last neutrophil
                  infusion)

             However, the plt and ANC requirements can be waived if low counts thought to be
             secondary to leukemia or tumor bone marrow infiltration

          9. Reproductive function:

               1. Female patients of childbearing potential must have a negative serum pregnancy
                  test confirmed within 7 days prior to enrollment

               2. Female patients with infants must agree not to breastfeed their infants while on
                  the study

               3. Male and female patients of child-bearing potential must agree to use an
                  effective method of contraception approved by the investigator during the study
                  and for a minimum of 3 months after study treatment

         10. Written informed consent

        Exclusion Criteria:

          1. Prior treatment with carfilzomib

          2. Known allergy to Captisol® (a cyclodextrin derivative used to solubilize carfilzomib).

          3. Down syndrome

          4. Fanconi Anemia or other underlying bone marrow failure syndrome

          5. Pregnant or lactating females

          6. Known history of Hepatitis B or C or HIV

          7. Patient with any significant concurrent illness

          8. Patient with uncontrolled systemic fungal, bacterial, viral or other infection with
             ongoing signs/symptoms despite appropriate treatment

          9. Patient with illness, psychiatric disorder or social issue that could compromise
             patient safety or compliance with the protocol treatment or procedures, or interfere
             with the consent, study participation, follow-up, or interpretation of study results.