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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 blood cell count (WBC) is elevated due to an increase in neutrophils and their precursors, and often also eosinophils and basophils [1, 2] (Figs 6.1, 6.2, 6.3). Marked eosinophilia is not usual. Granulocyte precursors are 10–20% of leucocytes. Monocytes are increased but less so than in chronic myelomonocytic leukaemia (CMML), typically being 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, the acquired Pelger-Huët anomaly (Fig. 6.4), 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 6.1

Peripheral blood film of a patient with aCML who had a very high WBC and presented with features of hyperviscosity, showing mainly neutrophil precursors. May-Grünwald-Giemsa (MGG), high power.

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Figure 6.2

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 6.3

Peripheral blood film of a patient with aCML (same patient as Fig. 6.2), 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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Figure 6.4

Peripheral blood film of a patient with aCML showing three dysplastic neutrophils. There is one ring neutrophil, a bilobed Pelger neutrophil and a non-lobed Pelger neutrophil. Note that all the neutrophils have abnormally coarse chromatin clumping. MGG, high power.

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Bone marrow cellularity is increased due to an increase in cells of granulocyte lineage (Figs 6.5 and 6.6). All lineages may show dysplasia, which may include ring sideroblasts and dysplastic megakaryocytes including micromegakaryocytes. Blast cells are, by definition, less than 20%. Trephine biopsy sections show similar features ...

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