Extramedullary blast crisis of CD34+ CD38- leukemia stem cells in chronic myeloid leukemia resistant to tyrosine kinase inhibitors: a report of two cases

We report two cases of chronic-phase chronic myeloid leukemia (CML), who presented extramedullary blast crisis; biopsy revealed proliferation of uniform blast cells, and immunophenotype was suggestive of CD34+ primitive hematopoietic cells. The BCR/ABL fusion gene detected in a paraffin-embedded section of the lesion by double-color fluorescence in situ hybridization (FISH), indicating an extramedullary tumor composed of CML leukemia stem cells in both cases. Although treated with dasatinib, systemic chemotherapy, and local radiotherapy, both patients died of infection-related complications. Therefore, in our cases, CD34+ CD38leukemia stem cells of CML appear to have migrated to and proliferated in extramedullary sites. Once blast crisis develops, the prognosis is very poor, more potent tyrosine kinase inhibitors such as dasatinib will be ineffective, and a transplant of human stem cells may be needed.