What is the incidence of myeloid (Myeloblastic) blast crisis vs lymphoid (Lymphoblastic) blast crisis in Chronic Myeloid Leukemia (CML)?

Incidence of Myeloid vs Lymphoid Blast Crisis in CML

In chronic myeloid leukemia (CML), myeloid blast crisis accounts for 70-80% of cases while lymphoid blast crisis represents 20-30% of cases. 1

Understanding Blast Crisis in CML

Blast crisis (BP) represents the terminal phase in the natural progression of CML, characterized by:

• ≥30% blasts in peripheral blood or bone marrow, or extramedullary blastic infiltration 1
• Transformation from chronic phase (CP) to blast phase (BP) occurs due to genetic instability in BCR-ABL-positive cells 1
• Additional chromosomal abnormalities often develop during progression to blast crisis 2

Distinguishing Between Myeloid and Lymphoid Blast Crisis

Diagnostic Methods

• Immunohistochemistry with antibodies against CD34, TdT, myeloid, monocytic, erythroid, B and T-lymphoid cell markers helps distinguish between the two types 1
• Flow cytometry and histochemistry provide accurate assessment of immature cells and lineage determination 1

Characteristics of Myeloid Blast Crisis (70-80% of cases)

• Typically expresses myeloid markers including CD33, CD13, CD38, CD34, CD11b, and HLA-DR 3
• Higher frequency of eosinophils and basophils in peripheral blood 3
• Poorer prognosis compared to lymphoid blast crisis 2
• May show additional chromosomal aberrations beyond Philadelphia chromosome 3

Characteristics of Lymphoid Blast Crisis (20-30% of cases)

• Most commonly presents as B-cell ALL with expression of CD10, CD19, CD34, and HLA-DR 3
• Lower percentage of eosinophils and basophils in peripheral blood 3
• May occasionally co-express myeloid markers (CD13, CD33) 3
• Higher ratio of blasts in bone marrow compared to peripheral blood 3

Clinical Implications and Management

• Both types of blast crisis represent a significant therapeutic challenge with poor outcomes 4
• Treatment approach includes:
  • Tyrosine kinase inhibitor (TKI) therapy based on mutation profile 4
  • Possible addition of chemotherapy appropriate for the blast lineage 5, 6
  • Goal of achieving second chronic phase to proceed to allogeneic stem cell transplantation 4
• Survival outcomes:
  • No significant difference in overall survival between lymphoid and myeloid blast crisis 3
  • Patients treated with TKIs have better survival than those without TKI treatment 3
  • Allogeneic stem cell transplantation offers the best chance for long-term survival 4

Prevention and Monitoring

• Early and rigorous elimination of BCR-ABL through effective TKI therapy in chronic phase is crucial for prevention 4
• Regular monitoring for early response indicators helps identify patients who may need alternative therapies or early transplantation 4
• Despite advances in TKI therapy for chronic phase CML, blast crisis remains a major challenge with limited treatment options 6