Leukemia SPORE Phase II DAC Study for R/R and Elderly Acute AML and MDS

Study Groups: If the participant is found to be eligible to take part in this study and he/she is one of the first 30 participants enrolled, the participant will have an equal chance of being in one of 3 study groups. If the participant enrolls after the first 30 participants are enrolled, he/she will have a higher chance of being assigned to the group is having better results. * If participant is in Group 1, he/she will receive decitabine alone. * If participant is in Group 2, he/she will receive decitabine and carboplatin. * If participant is in Group 3, he/she will receive decitabine and arsenic trioxide. Study Drug Administration: Every 4 weeks is a study cycle. The participant will receive decitabine by vein over about 1 hours on Days 1-5 of each cycle. If the participant is receiving carboplatin, he/she will receive it over 1 hour on Day 8 (+/-2 days) of each cycle. If the participant is receiving arsenic trioxide, he/she will receive it over about 1 hour on Days 1-5 of each cycle Study Visits: Blood (about 1-2 teaspoons) will be drawn 1-2 times a week during Cycle 1 and then every 2-4 weeks after that for routine tests. If you have stable disease, blood will only be drawn every 4-6 weeks. On Day 28 of Cycle 3 (+/- 3 days), the participant will have a bone marrow aspirate and biopsy to check the status of the disease. After that, the participant will have bone marrow biopsies/aspirations when the doctor thinks it is needed. If the participant is in Group 3, he/she will have EKGs on Day 1 of each cycle before receiving the study drugs. On Days 1 and 4 of each cycle, blood (about 1-2 teaspoons) will also be drawn for routine tests before their dose of the study drugs. If the participant is taken off study, blood (about 1-2 teaspoons) will be drawn for routine tests. Length of Study: The participant may continue taking the study drugs for as long as the doctor thinks it is in your best interest. The participant will no longer be able to take the study drug(s) if the disease gets worse, if intolerable side effects occur, or if he/she is unable to follow study directions. This is an investigational study. Arsenic trioxide is FDA approved and commercially available for the treatment of APL. Decitabine is FDA approved and commercially available for the treatment of MDS. Carboplatin is FDA approved and commercially available for the treatment solid tumors. The study drug or study drug combination the participant receives on this study are considered investigational.