Pathobiology of lymphoid and myeloid blast crisis and management issues

Despite recent improvements in the treatment of early-stage disease, the blastic phase of chronic myeloid leukemia (CML) remains a therapeutic challenge. For imatinib-naïve patients, imatinib provided encouraging hematologic and cytogenetic benefits; however, the vast majority of CML blast crisis cases today arise in patients already on imatinib-based therapy. Clonal evolution and duplication of the Philadelphia chromosome continue to be associated with blastic phase transformation, but recent studies have identified BCR/ABL kinase domain mutations in 30%-40% of blast crisis patients. This implies that BCR-ABL-targeted therapy might have influenced the molecular road map to blastic transformation. In this review, we will examine the effect of imatinib on primitive CML progenitors and how this might influence the pathophysiology of blast crisis. A rational framework for deciding how best to integrate stem cell transplantation, traditional chemotherapy, imatinib, and other BCR-ABL kinase inhibitors in the care of blast crisis patients will also be discussed.