Platelet count > 75,000/uL The platelet count must be > 75,000 mm^3 prior to starting every cycle of treatment with decitabine; decitabine may be delayed for up to 4 weeks between cycles (i.e. may be administered as infrequently as every (q) 8 weeks) while waiting for counts to recover Peripheral platelet count (PLT) >= 75,000/mm^3 Platelet count >= 100,000/uL (transfusion independent) STEP I: Untransfused platelet count >= 75,000 cells/mm^3 (obtained within 28 days prior to randomization) Platelet count >= 75,000/uL (transfusion independent) Patients must have a peripheral blast count < 25,000/uL within 2 days prior to registration; (treatment with hydroxyurea and steroids is permitted to bring the countdown) Platelet count >= 75,000/mm^3 within 90 days prior to randomization Platelet count >= 75,000 and transfusion independent Platelet count >= 75,000/mm^3 Lymphocyte count > 1,000/mcL NOTE: Patients with documented bone marrow involvement by lymphoma are not required to meet the above hematologic parameters, but must have a platelet count of at least 75,000/mcL and neutrophil count of at least 1,000/mcL Platelets >= 75,000 cells /uL (unsupported, defined as no platelet transfusion within 7 days) INCLUSION CRITERIA FOR STRATUM C: Platelets >= 75,000 cells/uL (unsupported, defined as no platelet transfusion within 7 days) Circulating blast count >= 50,000/uL within the week preceding enrollment Within 14 days of registration: Platelet count >= 75,000/mm^3 Platelet count >= 50,000/uL Platelet count >= 75,000/uL Platelet count >= 75,000/mcL; must be obtained within 28 days prior to registration RECURRENT/ PROGRESSIVE DIPG (STRATUM 1): Platelets >= 100,000/mm^3 (unsupported, defined as no platelet transfusion within 7 days, and recovery from post-transfusion nadir) NON-PROGRESSED DIPG (STRATUM 2): Platelets >= 100,000/ mm^3 (unsupported, defined as no platelet transfusion within 7 days, and recovery from post-transfusion nadir) Platelet count >= 100,000/uL (transfusion independent) Platelet count >= 50,000/uL for patients with solid tumors and known bone marrow metastatic disease Platelet count >= 100,000 mm^3; platelets >= 75,000 required for patients who received cycle 1 of mFOLFOX6 prior to registration Platelet count >= 75,000/mm^3