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Myelodysplastic/ Myeloproliferative Neoplasms Treatment (PDQ®): Treatment - Health Professional Information [NCI] - Atypical Chronic Myelogenous Leukemia

Disease Overview

Atypical chronic myelogenous leukemia (aCML) is a leukemic disorder that exhibits both myelodysplastic and myeloproliferative features at the time of diagnosis.

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Atypical CML is characterized pathologically by the following:[1]

  • Peripheral blood leukocytosis with increased numbers of mature and immature neutrophils.
  • Prominent dysgranulopoiesis.
  • No Philadelphia chromosome or BCR/ABL fusion gene.
  • Neutrophil precursors (e.g., promyelocytes, myelocytes, and metamyelocytes) accounting for more than 10% of white blood cells.
  • Minimal absolute basophilia with basophils accounting for less than 2% of white blood cells.
  • Absolute monocytosis with monocytes typically account for less than 10% of white blood cells.
  • Hypercellular bone marrow with granulocytic proliferation and granulocytic dysplasia.
  • Fewer than 20% blasts in the blood or bone marrow.
  • Thrombocytopenia.

Clinical features of aCML include the following:[1,2,3,4]

  • Anemia. (Refer to the PDQ summary on Fatigue for more information on anemia.)
  • Thrombocytopenia.
  • Splenomegaly (in 75% of cases).

Although cytogenetic abnormalities are found in as many as 80% of the patients with aCML, none is specific.[1,2,3,5] No Philadelphia chromosome or BCR/ABL fusion gene exists.

The exact incidence of aCML is unknown. The median age at the time of diagnosis of this rare leukemic disorder has been reported to be in the seventh or eighth decade of life.[1,2,3]

Morphologically, aCML is characterized by myelodysplasia associated with bone marrow and peripheral blood patterns similar to chronic myelogenous leukemia, but cytogenetically it lacks a Philadelphia chromosome or BCR/ABL fusion gene.[1] The white blood cell count in the peripheral blood is variable. Median values range from 35 × 109 /L to 96 × 109 /L, and some patients may have white blood cell counts greater than 300 × 109 /L.[1,2,3,5] Blasts in the peripheral blood typically account for less than 5% of the white blood cells. Immature neutrophils usually total 10% to 20% or more.[1] The percentage of monocytes is rarely more than 10%. Minimal basophilia may be present.[1,2,3,5] Nuclear abnormalities, such as acquired Pelger-Huët anomaly, may be seen in the neutrophils. Moderate anemia (often showing changes indicative of dyserythropoiesis) and thrombocytopenia are common.[1,2,3,4] Bone marrow findings include the following: [1,2,3,5]

  • Granulocytic hypercellularity.
  • Blast count less than 20%.
  • Dysgranulopoiesis
  • Megakaryocytic dysplasia.
  • Erythroid precursors accounting for more than 30% of marrow cells with dyserythropoiesis present (in some cases).
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