[Initial presentation of lymphoblastic crisis in a pediatric chronic myelogenous leukemia patient].

A 9-year-old girl was referred to our hospital because of facial palsy. Both physical and blood examination revealed hepatosplenomegaly and leukocytosis, respectively. A bone marrow examination demonstrated marked hypercellularity involving myeloblasts and lymphoblasts. Based on these results, we suspected mixed phenotype acute leukemia. However, her leukemic blasts expressed B-cell antigens, and a chromosomal analysis of her bone marrow cells revealed the following karyotype: 46, XX, t (9;22) (q34;q11.2). All her neutrophils were positive for the breakpoint cluster region-Abelson murine leukemia viral oncogene homolog 1 fusion protein. Based on these findings, she was diagnosed with a lymphoblastic crisis of chronic myelogenous leukemia (CML). Combined chemotherapy, involving imatinib, resulted in complete molecular remission. She received cord blood transplant (CBT) during the first complete remission; she is alive and has not suffered a relapse since two years after the CBT. The sudden onset of a blastic crisis in pediatric CML is rare, and it may be difficult to distinguish such cases from de novo Ph-positive leukemia. For diagnostic purposes, it is essential to consider a patient's clinical course and blood test results.