Disease Overview

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

Atypical CML is characterized pathologically by:[1]

Clinical features of aCML include:[1-4]

Although cytogenetic abnormalities are found in as many as 80% of the patients with aCML, none is specific.[1-3,5] No Philadelphia chromosome or BCR::ABL1 gene fusion is present.

The exact incidence of aCML is unknown. The median age at the time of diagnosis of this rare leukemic disorder is in the seventh or eighth decade of life.[1-3]

Morphologically, aCML is characterized by myelodysplasia associated with bone marrow and peripheral blood patterns similar to chronic myeloid leukemia, but cytogenetically it lacks a Philadelphia chromosome or BCR::ABL1 gene fusion.[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.[1-3,5] 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.[1-3,5] 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.[1-4] Bone marrow findings include: [1-3,5]

The median survival times for aCML are reported to be less than 20 months, and thrombocytopenia and marked anemia are poor prognostic factors.[1,2] Atypical CML evolves to acute leukemia in approximately 25% to 40% of patients.[1,3] In the remaining patients, fatal complications include resistant leukocytosis, anemia, thrombocytopenia, hepatosplenomegaly, cerebral bleeding associated with thrombocytopenia, and infection.[3,4]