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Introduction

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Atypical chronic myeloid leukaemia (aCML) is a Ph-negative, BCR-ABL1-negative haematological neoplasm characterized by leucocytosis, an increase of granulocyte precursors in the peripheral blood and dysplastic features. In the World Health Organization (WHO) classification it is categorized as one of the myelodysplastic/myeloproliferative neoplasms (MDS/MPN).

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Clinical features

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Patients may present with symptoms of anaemia or with infection or bruising. The spleen may be enlarged and less often the liver. aCML is mainly a disease of the elderly. It is a rare condition.

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Haematological and pathological features

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The white cell count (WBC) is increased due to an increase in neutrophils and their precursors and often also eosinophils and basophils [1, 2] (Figures 13.1, 13.2, 13.3). Marked eosinophilia is not usual. Granulocyte precursors are 10-20% of leucocytes. Monocytes are increased but less so than in chronic myelomonocytic leukaemia (CMML), being usually less than 10%. There is usually anaemia and there may also be thrombocytopenia. Peripheral blood cells usually show dysplastic features such as macrocytosis, hypogranular neutrophils, acquired Pelger-Huët anomaly and platelet anisocytosis, but sometimes dysplastic features are very minor. A minority of patients have abnormal chromatin clumping in neutrophils, sometimes together with hypolobation or hypogranularity. A few blast cells may be present but they are usually less than 5% and, by definition, always less than 20%.

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Figure 13.1

Peripheral blood film of a patient with aCML who had a very high white cell count and presented with features of hyperviscosity, showing mainly neutrophil precursors. MGG, high power.

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Figure 13.2

Peripheral blood film of a patient with aCML, showing a dysplastic neutrophil, a myelocyte and a monocyte. There is also anisocytosis and stomatocytosis. MGG, high power.

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Figure 13.3

Peripheral blood film of a patient with aCML (same patient as Figure 13.2), showing a basophil, a myelocyte and two monocytes, one of which is immature. There is also anisocytosis and a very bizarre platelet. MGG, high power.

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Bone marrow cellularity is increased due to an increase in cells of granulocyte lineage (Figures 13.4 and 13.5). All lineages may show dysplasia, which may include ring sideroblasts and dysplastic megakaryocytes including micromegakaryocytes. Blast cells are, by definition, less than 20%. The trephine biopsy shows similar features (Figure 13.6). Reticulin deposition may be increased (Figure 13.7).

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Figure 13.4

Bone marrow aspirate film of a patient with aCML (same patient as Figure 13.2), showing hypercellularity. MGG, low power.

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Figure 13.5

Bone marrow aspirate film of a patient ...

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