Chronic myelomonocytic leukaemia (CMML) is a Philadelphia-negative BCR-ABL1-negative haematological neoplasm characterized by both dysplastic features and proliferative features (monocytosis and sometimes neutro -philia). It is therefore classified in the World Health Organization (WHO) classification as one of the myelodysplastic/myeloproliferative neoplasms. In the French-American-British (FAB) classification it was included in the category of myelodysplastic syndromes (MDS). The clinical and haematological features cover a spectrum from predominantly myelodysplastic to predominantly myeloproliferative.
CMML is mainly a disease of the elderly with a moderate male predominance. Some patients present with symptoms of anaemia, low grade fever and night sweats, weight loss or bleeding. In others the diagnosis is incidental. Splenomegaly is sometimes detected. Hepatomegaly, lymphadenopathy and skin infiltration are less common. Organomegaly is more common in patients with a high white blood cell count (WBC). Serous effusions are occasionally seen.
Haematological and pathological features
There is usually anaemia and sometimes there is macrocytosis. There may be leucopenia or leucocytosis. By definition, the monocyte count is more than 1 × 109/l and monocytes are usually more than 10% of leucocytes. In some patients the monocytes are all mature, but in others there are immature or cytologically abnormal monocytes, e.g. with cytoplasmic basophilia, heavy granulation or hypersegmented nuclei (Figs 5.1 and 5.2). Cells of other lineages may show dysplastic features (Fig. 5.3). There may be small numbers of circulating blast cells and promonocytes but they do not exceed 20%. It is important not to misidentify immature monocytes as promonocytes or a misdiagnosis of acute myelomonocytic leukaemia may occur. In some patients there is also neutrophilia. Neutropenia can also occur. Neutrophil precursors are generally less than 10% of leucocytes. Occasionally the eosinophil count is increased but, in the 2008 WHO classification, cases with rearrangement of PDGFRB are excluded from the category of CMML. The platelet count may be normal or reduced. The monocytes express non-specific esterases, e.g. alpha naphthyl acetate esterase and alpha naphthyl butyrate esterase.
Peripheral blood film of a patient with CMML showing a neutrophil and three abnormal monocytes. May-Grünwald-Giemsa (MGG), high power.
Peripheral blood film of a patient with CMML showing two abnormal monocytes. MGG, high power.
Peripheral blood film of a patient with CMML (same patient as Fig. 5.1) showing a band form, a hypogranular neutrophil, a neutrophil with an abnormally shaped nucleus, a large hypogranular platelet and poikilocytes including acanthocytes. MGG, high power.
The bone marrow is hypercellular. Increased granulopoiesis is common. Sometimes abnormal monocytes and their precursors are prominent, but this is not always so ...