Diagnosing and managing advanced chronic myeloid leukemia

Clinical staging of chronic myeloid leukemia (CML) distinguishes between chronic phase (CP-CML), accelerated phase (AP-CML), and blastic phase (BP-CML), reflecting its natural history in the absence of effective therapy. Morphologically, transformation from CP-CML to AP/BP-CML is characterized by a progressive or sudden loss of differentiation. Multiple different somatic mutations have been implicated in transformation from CP-CML to AP/BC-CML, but no characteristic mutation or combination of mutations have emerged. Gene expression profiles of AP-CML and BP-CML are similar, consistent with biphasic evolution at the molecular level. Gene expression of tyrosine kinase inhibitor (TKI)-resistant CP-CML and second CP-CML resemble AP/BP-CML, suggesting that morphology alone is a poor predictor of biologic behavior. At the clinical level, progression to AP/BP-CML or resistance to first-line TKI therapy distinguishes a good risk condition with survival close to the general population from a disease likely to reduce survival. Progression while receiving TKI therapy is frequently caused by mutations in the target kinase BCR-ABL1, but progression may occur in the absence of explanatory BCR-ABL1 mutations, suggesting involvement of alternative pathways. Identifying patients in whom milestones of TKI response fail to occur or whose disease progress while receiving therapy requires appropriate molecular monitoring. Selection of salvage TKI depends on prior TKI history, comorbidities, and BCR-ABL1 mutation status. Despite the introduction of novel TKIs, therapy of AP/BP-CML remains challenging and requires accepting modalities with substantial toxicity, such as hematopoietic stem cell transplantation (HSCT).