Peripheral blood
The peripheral blood shows a leukocytosis and includes neutrophils at different stages of maturation (including myelocytes, metamyelocytes, promyelocytes), an absolute basophilia, and, commonly, eosinophilia.
Aspirate smear
Bone marrow evaluation shows increased cellularity due to granulocytic hyperplasia with a spectrum of maturation. Megakaryocytes in CML are characterized by decreased size and hypolobated nuclei ("dwarf megakaryocytes").
Pseudo-Gaucher cells
Pseudo-Gaucher cells and sea-blue histiocytes can be seen due to increased cell turnover.
Cytogenetics
Chronic myelogenous leukemia is defined by the BCR-ABL1 fusion gene. Most cases have the characteristic t(9;22)(q34;q11.2) identified by routine cytogenetic analysis.
Blast phase
CML can progress to a blast phase defined by >20% blasts in the peripheral blood or bone marrow or by an extramedullary blast proliferation. The blast lineage may be myeloid or lymphoid.
