 - Cohort A: Diagnosis of AML by World Health Organization WHO criteria, either relapsed or refractory; acute promyelocytic leukemia Acute promyelocytic leukemia with t15;17q22;q12 and variants will be eligible only after failure of a regimen containing arsenic trioxide; patients in this cohort must have had an initial remission duration of 1 year and cannot have received any prior salvage chemotherapy 