Administration of imatinib after allogeneic hematopoietic stem cell transplantation may improve disease-free survival for patients with Philadelphia chromosome-positive acute lymphobla stic leukemia

Background: Maintenance therapy with imatinib during the post-transplant period has been used for patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph + ALL); however, its efficacy has not been demonstrated. A study was designed to investigate the safety of imatinib and its efficacy in preventing hematological relapse and improving disease-free survival (DFS) when administered after allogeneic hematopoietic stem cell transplantation (allo-HCT). Methods: Patients with Ph + ALL that received allo-HCT were enrolled in the study. Real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was used to detect BCR-ABL transcript levels. Imatinib therapy was initiated if patient neutrophil counts were > 1.0 x 10(9)/L and platelet counts were > 50.0 x 10(9)/L, or if they displayed either elevated BCR-ABL transcript levels in two consecutive tests, or a BCR-ABL transcript level >= 10(-2) after initial engraftment. Patients receiving imatinib after relapse were assigned to the non-imatinib group. The imatinib treatment was scheduled for 3-12 months, until BCR-ABL transcript levels were negative at least for three consecutive tests or complete molecular remission was sustained for at least 3 months. Results: A total of 82 patients were enrolled. Sixty-two patients initiated imatinib therapy post-HCT. Imatinib therapy was initiated at a median time of 70 days post-HCT. Grade 3-4 adverse events (AEs) occurred in 17.7% of patients. Ten patients (16.1%) terminated imatinib therapy owing to AEs. Among the patients in imatinib and non-imatinib groups, the estimated 5-year relapse rate was 10.2% and 33.1% (p = 0.016), and the 5-year probability of DFS was 81.5% and 33.5% (p = 0.000) with the median follow-up of 31 months (range, 2.5-76 months) and 24.5 months (range, 4-72 months), respectively. Multivariate analysis identified imatinib maintenance therapy post-HCT as an independent prognostic factor for DFS (p = 0.000, hazard ratio [HR] = 4.8) and OS (p = 0.000, HR = 6.2). Conclusions: These results indicate that relapse rate can be reduced and DFS may be improved in Ph + ALL patients with imatinib maintenance therapy after HCT. BCR-ABLmonitoring by qRT-PCR can guide maintenance therapy with imatinib including initiation time and treatment duration after allo-HCT.