A Pilot Study Evaluating the Safety and Efficacy of Imatinib Given Early after Transplant for High-Risk Philadelphia Chromosome-Postive Leukemias.

Patients with Ph+ acute lymphoblastic leukemia (ALL) or chronic myelogenous leukemia (CML) in stages other than first chronic phase (CP1) frequently have recurrent malignancy after allogeneic hematopoietic cell transplant (HCT). Imatinib given after HCT for the treatment of hematological relapse has been of limited success in Ph+ALL but may induce more durable remissions in CML.

Hypothesis: We postulated that imatinib might be most effective for preventing hematological relapse after myeloablative HCT if given immediately after engraftment to patients without detectable leukemia, or with leukemia that can be detected only at the molecular level.

Study design: A pilot study is ongoing to evaluate the safety and preliminary efficacy of imatinib begun early after myeloablative HCT and continued until post-transplant day 365 (D+365). Study participants became eligible to start imatinib (adults 400 mg/day, children 260 mg/m²/day) if the residual marrow leukemia burden at the time of initial engraftment (ANC>500 on 2 consecutive days) did not exceed >1/20 Ph+ metaphases, >1% aberrant antigen expression on blasts by multidimensional flow, or presence of bcr/abl in >5% interphase nuclei by FISH. The primary endpoint of safety was defined by ability to tolerate imatinib (adults ≥200 mg/day, children ≥100 mg/day) for ≥ 6 days/week until D+90. An attempt was made to administer higher daily doses of imatinib after D+90.

Patient characteristics: Ten patients with Ph+ALL (8 CR1, 2 CR2) and 6 patients with CML (2 AP, 2 CP2, 2 CP3) have been enrolled; 13/16 had leukemia detected by molecular or cytogenetic methods at the time of transplant. Median age at transplant was 40 y (range 5–62 y). Stem cell sources were cord blood (n=1), marrow (n=4) or G-mobilized peripheral blood (n=11). Donors were unrelated (n=10) or related (n=6).

Results: Imatinib therapy began in 15 patients at a median of 29 days (range 24–39 days) after HCT and has been administered for a median of 299 days (range, 33–380 days). The median of average daily doses during this time period was 400 mg/day (range 389 to 510 mg/day) among adults and 304 mg/m²/day for the 2 children. All patients tolerated imatinib at the intended dose intensity within the first 90 days after HCT. Toxicities (NCI CTC v3.0) possibly attributed to imatinib included grade 1–2 nausea (n=3), grade 1 edema (n=3), grade 1–2 anemia (n=2), and grade 3 neutropenia (n=2). Per protocol, one patient with neutropenia received 2 doses of G-CSF at D+75 and continued imatinib without neutropenia. The second patient was not given G-CSF and imatinib was held for 2 weeks from D+160 until the ANC was >2000. All patients are surviving at a median of 333 days after HCT (range, 68–564), and 14/15 patients have no detectable bcr/abl transcripts in the blood or marrow. Seven patients (4 ALL, 3 CML) have completed imatinib therapy and survive at a median of 467 days after HCT (range, 410–564 days) and 6/7 have no detectable bcr/abl transcripts in blood or marrow. One patient (CML-CP3) with cytogenetic relapse at D+118 had a 4^th remission after withdrawal of immunosuppression and continued imatinib but developed hematological relapse at D+429.

Conclusions: We conclude that imatinib therapy can be safely prescribed early after myeloablative allogeneic HCT at a dose-intensity comparable to that used in general oncology. Preliminary efficacy data are encouraging and worthy of further study.