Outcome and prognostic factors of children with Philadelphia chromosome-positive acute lymphoblastic leukemia treated with imatinib followed by allogeneic hematopoietic cell transplantation in first remission

BACKGROUND: Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) is a subset of ALL with poor prognosis. Here, we analyzed the outcomes and prognostic factors of children with Ph+ ALL who received imatinib and chemotherapy followed by allogeneic hematopoietic cell transplantation (HCT) in first complete remission (CR). METHODS: Thirty-one Ph+ ALL patients (female 10) diagnosed from January 2005 to December 2016 were included in the study. All patients were treated with imatinib and chemotherapy before HCT. Bone marrow (BM) evaluations included real-time quantitative polymerase chain reaction (RQ-PCR) study of the BCR-ABL1 fusion transcript. All patients received HCT with total body irradiation (TBI)-based conditioning at a median of 6.4 (range, 4.2–47.1) months from diagnosis. RESULTS: Compared to values at diagnosis, the median decrement of RQ-PCR value post-consolidation, and prior to HCT was −3.7 Log and −4.8 Log, respectively. The 5-year event-free survival (EFS) and overall survival of the patients were 64.5±9.4% (20/31) and 75.0±8.3% (23/31) respectively. Events included relapse (N=5) and death in CR post-HCT (N=6). The 5-year incidence of molecular relapse was 30.9±9.1% (9/31). An RQ-PCR decrement of at least −4 Log post-consolidation significantly predicted lower incidence of molecular relapse: 7.7±7.7% for ≥−4 Log decrement, 50.0±13.8% for <−4 Log decrement (P=0.027). CONCLUSION: Decrement in RQ-PCR for the BCR-ABL1 transcript that was determined after consolidation was the only significant prognostic factor for incidence of molecular relapse. In the post-induction TKI initiation setting, steadfast imatinib treatment during consolidation may allow for optimum post-HCT outcomes.