Blood films display a range of abnormalities. A monocyte count of >1x109/L is essential for a diagnosis of<unk> . Other features may include; leukocytosis (50% of cases); left shift and dysplasia of monocytes and granulocytes; presence of metamyelocytes, myelocytes and promonocytes; monocytes with hypersegmented/abnormal shaped nuclei, increased cytoplasmic basophilia and/or the presence of cytoplasmic granules; eosinophilia (in cases of<unk>  with eosinophilia); and spherocytosis (in cases of direct Coombs test, DCT, positive haemolytic anaemia). Platelet counts may be reduced, increased or normal. Haemoglobin levels are usually reduced with normocytic and normochromic red blood cells. Autoantibodies and cold agglutinins may be present and 10% of<unk>  is DCT positive. Bone marrow aspirates will display hypercellularity with increased counts of granulocytic and monocytic cells. Bone marrow core biopsies may show a predominance of myelocytic and monocytic cells, abnormal localisation of immature precursors and dysplastic megakaryocytes. Monocytic nodules are a common feature in biopsies. The phenotypical characteristics of<unk>  are; CD11b, CD11c, CD14, CD33, CD45 and CD64 seen in 100% of cases; CD13 found in 95% of cases; CD4 found in 76% of cases; HLA-DR found in 71% of cases; CD56 found in 53% of cases; CD2 found in 34% of cases; CD16 found in 29% of cases; CD10 found in 28% of cases; CD23 and CD7 found in 9% of cases; and CD117 found in 5% of cases. Classification Haematopoiesis. The two lineages of myeloid and lymphoid cells are formed from haematopoietic stem cells. Leukemia subtypes are categorised into single clinical entities so that they can be diagnosed and treated appropriately. Leukaemias are subdivided into lymphoid and myeloid neoplasms, depending on which bone marrow cells are cancerous. The myeloid neoplasms contain acute and chronic leukemias, myelodysplastic syndromes (MDSs) and myeloproliferative neoplasms (MPNs). MPNs are characterised by increased production of myeloid blood cells, with a higher than normal number of mature cells. Unlike MPNs, MDSs have a dysfunctional production of myeloid cells with a reduced number of mature cells. Many of the cells produced in MDS are abnormal looking, known as dysplasia.<unk>  shows characteristics of both groups and thus is a difficult disease to categorise. FAB classification The French-American-British (FAB) classification system was published in 1976 to classify the leukaemias. It placed<unk>  into the category of MDS, along with the refractory anaemia, refractory anaemia with ring sideroblasts, refractory anaemia with excess blasts and refractory anaemia with excess blasts in transformation. The system does have clinical utility; however factors such as cytogenetic status are not within the remit of the classification. For this reason, many disease entities in these groups show a great deal of heterogeneity. WHO classification In 2001, the WHO Classification of Myeloid Neoplasms was published, classifying<unk>  into a new group of diseases, the myelodysplastic/myeloproliferative neoplasms (MDS/MPN), reflecting the disease's neoplastic nature. Other diseases in this category are juvenile myelomonocytic leukaemia, atypical CML; BCR-ABL1 negative and MDS/MPD unclassifiable. These MDS/MPN overlap syndromes have effective production of some lineages of blood cells, but show ineffective proliferation of other lineages. The 2008 revision of the classification moved cases of<unk>  with PDGFR gene translocations to a new group, myeloid/lymphoid neoplasms with eosinophilia with abnormalities of PDGFRA, PDGFRB or FGFR1. Diagnostic criteria FAB criteria The FAB criteria for diagnosis are as follows: *Monocyte count >1x109/L *0–19% blasts in bone marrow *9 is used as a cut-off to differentiate the two. WHO criteria The WHO criteria for diagnosis are as follows: *Persistent peripheral blood monocytosis with counts >1x109/L *No Philadelphia chromosome or BCR-ABL1 fusion gene *No rearrangement of PDGFRA or PDGFRB gene *1.5x109/L. Presence of two or more phenotypic abnormalities can aid a diagnosis of<unk>  in the absence of identifying cytogenetic or dysplastic features. These can include the expression of CD56 and/or CD2, or under-expression of HLA-DR.
Chronic myelomonocytic leukemia
Prolymphocytic leukemia
Large granular lymphocytic leukemia
Chronic neutrophilic leukemia
Acute myelomonocytic leukemia
Mixed-phenotype acute leukemia
Atypical chronic myeloid leukemia
Acute myeloblastic leukemia with maturation