CML in Blast Phase

CML in blast phase can occur de novo or can evolve while on treatment with a tyrosine kinase inhibitor. The blasts can be of myeloid or lymphoid lineage. It carries a poor prognosis and the aim of treatment is to induce remission/chronic phase, followed by consolidation with allogeneic haematopoietic cell transplantation.

Diagnostic Criteria (WHO 2016)

• ≥20% blasts in the blood or bone marrow or
• Presence of an extramedullary proliferation of blasts
• Presence of the t(9;22) translocation or BCR/ABL fusion gene

Peripheral blood film of a patient with CML in blast phase. Note the marked granulocytosis. There is a significant myeloblast population.

Blood Film Features:

• Marked leucocytosis involving various stages of granulocytic maturation
• Blast ≥ 20% blasts: may be of myeloid or lymphoid lineage
  • Myeloid lineage blast: may include neutrophilic, monocytic, megakaryocytic, basophilic, eosinophilic, or erythroid blasts
  • Lymphoid blast

Bone marrow aspirate of a patient with CML in blast phase.

Bone Marrow Features:

• Bone marrow is markedly hypercellular
• Blast ≥ 20% blasts: may be of myeloid or lymphoid lineage

Other Resources

• ASH image bank: CML-Blast Phase – Extramedullary Myeloid Tumor
• ASH image bank:  CML-Blast Phase