Lymphoblastic predominance of blastic phase in children with chronic myeloid leukaemia treated with imatinib: A report from the I-CML-Ped Study

Background: Chronic myeloid leukaemia (CML) is a rare disease in children. The frequency and outcome of children evolving to accelerated phase (AP) or blastic phase (BP) under treatment with imatinib is unknown. The aim of the current study is to assess the incidence of progression from CML in chronic phase with imatinib frontline in a paediatric setting and describe the management and outcome of these patients. Patients and methods: In the I-CML-Ped Study database (www.clinicaltrials.gov, #NCT01281735), 19 of 339 paediatric patients in chronic phase treated with imatinib in the frontline evolved to CML-AP or CML-BP. Results: With a median follow-up of 38 months (range: 2–190 months), the cumulative incidence of progression at 1 and 3 years was 3% (confidence interval [CI] 95%: 1–5%) and 7% (CI 95%: 4–11%), respectively. We observed a large predominance of lymphoid-BP (70%) over myeloid-BP (30%) with imatinib in frontline therapy. Sixteen patients underwent haematopoietic stem cell transplantation, and eight were treated with a tyrosine kinase inhibitor after transplant. Only the transplanted patients are alive. The 5-year overall survival rate of children with CML-AP/BP is 44%, with no statistical difference between the lymphoid-BP and myeloid-BP outcome. Conclusion: Children evolving to AP or BP under treatment with imatinib have a very poor prognosis with an overall survival under 50%, much worse than children with advanced phase at diagnosis.