Bone Marrow, Atypical chronic myeloid leukemia, H&E stain

Atypical CML (aCML) is a rare type of myelodysplastic/myeloproliferative neoplasm that resembles chronic myeloid leukemia but lacks the pathognomonic BCR-ABL1 rearrangement and encompasses dysplastic features.

Peripheral blood morphology shows high white cell count >13x109/L with left shift and dysplastic features of neutrophils, such as abnormally clumped chromatin and hypogranularity. Basophilia is absent or minimal. Monocyte count might be increased but it is always less than 10% of the WBC. This is especially important to differentiate it from Chronic myelomonocytic leukemia. Hemoglobin levels and platelet count vary but anemia and thrombocytopenia are not uncommon.

Bone marrow shows hypercellularity due to expanded granulopoiesis. Dysgranulopoiesis is similar to the peripheral blood but multilineage dysplasia could be present as well. Blast percentage may be increased but should be