Incorporation of imatinib into chemotherapeutic regimens has improved the prognosis of children with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL). We investigated a role of imatinib immediately before hematopoietic stem cell transplantation (HSCT). Children with Ph+ALL were enrolled on JPLSG Ph+ALL 04 Study within 1 week of initiation of treatment for ALL. Treatment regimen consisted of Induction phase, Consolidation phase, Reinduction phase, 2 weeks of imatinib monotherapy phase, and HSCT phase (Etoposide+CY+TBI conditioning). Minimal residual disease (MRD), the amount of BCR-ABL transcripts, was measured with the real-time PCR method. The study was registered in UMIN-CTR: UMIN ID C000000290. Forty-two patients were registered and 36 patients (86%) achieved complete remission (CR). Eight of 17 patients (47%) who had detectable MRD at the beginning of imatinib monotherapy phase showed disappearance or decrease in MRD after imatinib treatment. Consequently, 26 patients received HSCT in the first CR and all the patients had engraftment and no patients died because of complications of HSCT. The 4-year event-free survival rates and overall survival rates among all the 42 patients were 54.1 ± 7.8% and 78.1 ± 6.5%, respectively. Four of six patients who did achieve CR and three of six who relapsed before HSCT were salvaged with imatinib-containing chemotherapy and subsequently treated with HSCT. The survival rate was excellent in this study although all patients received HSCT. A longer use of imatinib concurrently with chemotherapy should eliminate HSCT in a subset of patients with a rapid clearance of the disease.
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