Final Diagnosis -- Chronic Myelogenous Leukemia




The bone marrow is approaching 100% cellular and demonstrates increased maturing neutrophilic cells. These bone marrow findings, in conjunction with fluorescence in situ hybridization studies demonstrating the BCR/ABL gene rearrangement, are diagnostic of chronic myelogenous leukemia (CML). Blasts are mildly increased in the peripheral blood and bone marrow, and flow cytometric studies performed on both specimens demonstrate B-lymphoblasts with an abnormal precursor B phenotype, which represent approximately 5%, or less, of total events. The presence of increased immature B-cells is confirmed by immunohistochemical stains performed on the bone marrow biopsy.

According to the 2008 World Health Organization (WHO) Classification of Tumors of the Haematopoietic and Lymphoid Tissues [1], the finding of blasts in the blood or bone marrow of a patient with chronic phase CML should raise a concern for progression of the disease with either myeloid or lymphoid differentiation. The abnormal blast population in accelerated and blast phase is 10-19% and 20% or more, respectively, fulfilling the criteria for acute leukemia.

The significance of a small aberrant B lymphoblast population in patients with newly diagnosed chronic phase (CP) CML was recently studied by reviewing clinical follow up data and flow cytometric immunophenotypic data on the diagnostic bone marrow sample. Vrotsos, E et al [2]found that in CP CML, a small (<0.5%) abnormal B-lymphoblast population is present in a significant minority of diagnostic bone marrow samples, but does not inevitably herald progression to B-lymphoblastic blast phase. In contrast, El Rassi et al [3], found that the presence of aberrant lymphoid blast cell population (2%) at the time of the diagnosis of CP-CML appears to be associated with early progression to lymphoid blast crisis.

In our patient, the significance of this small proportion (approximately 4%) of abnormal B lymphoblasts is uncertain. Although the findings do not meet diagnostic criteria for blast crisis of CML, they are worrisome for B lymphoblastic disease progression.


  1. Swerdlow SH, C.E., Harris NL, Jaffe ES, Pileri SA, Stein H, Thiele J, Vardiman JW., WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. 4th ed. Vol. 2. 2008, Lyon: International Agency for Research on Cancer.
  2. Vrotsos, E., M. Gorgan, and J.A. DiGiuseppe, Detection of small abnormal B-Lymphoblast populations at diagnosis of chronic myelogenous leukemia, BCR-ABL1+: Incidence, phenotypic features, and clinical implications. Cytometry B Clin Cytom, 2015.
  3. El Rassi, F., et al., Predicting early blast transformation in chronic-phase chronic myeloid leukemia: is immunophenotyping the missing link? Cancer, 2015. 121(6): p. 872-5.

Contributed by Lama Farchoukh, MD and Fiona E. Craig, MD

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