Imatinib Mesylate After a Donor Stem Cell Transplant in Treating Patients With Philadelphia Chromosome-Positive Leukemia

DISEASE CHARACTERISTICS: Diagnosis of 1 of the following: Acute lymphoblastic leukemia or chronic myeloid leukemia (CML) characterized by p^190 and/or p^210 bcr/abl gene rearrangement Accelerated or blastic phase CML CML in second or greater chronic phase No imatinib mesylate-resistant leukemia Planned allogeneic hematopoietic stem cell transplantation Availability of an appropriately matched related or unrelated donor Autologous or nonmyeloablative transplantation is not allowed None of the following within 4 days after the date of neutrophil engraftment*: More than 5% marrow blasts Circulating peripheral blood leukemic blasts Aberrant antigen expression on marrow myeloblasts ≥ 1% by multidimensional flow cytometric assay Presence of bcr/abl in > 5% of marrow interphase nuclei by fluorescent in situ hybridization More than 1 of 20 Philadelphia chromosome-positive marrow metaphases CNS involvement by leukemia NOTE: *The date of neutrophil engraftment is defined as the second consecutive day at which the peripheral blood absolute neutrophil count exceeds 500/mm3 PATIENT CHARACTERISTICS: Performance status Not specified Life expectancy At least 2 months Hematopoietic See Disease Characteristics Absolute neutrophil count ≥ 1,200/mm^3 (use of filgrastim [G-CSF] allowed) Hepatic Not specified Renal Not specified Other Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No known imatinib mesylate hypersensitivity No other disease that severely limits life expectancy PRIOR CONCURRENT THERAPY: Biologic therapy See Disease Characteristics