Chronic myelomonocytic leukemia

Chronic myelomonocytic leukemia (CMML) is a type of leukemia, which are cancers of the blood-forming cells of the bone marrow. In adults, blood cells are formed in the bone marrow, by a process that is known as haematopoiesis. In CMML, there are increased numbers of monocytes and immature blood cells (blasts) in the peripheral blood and bone marrow, as well as abnormal looking cells (dysplasia) in at least one type of blood cell. Chronic myelomonocytic leukemia (CMML) is a type of leukemia, which are cancers of the blood-forming cells of the bone marrow. In adults, blood cells are formed in the bone marrow, by a process that is known as haematopoiesis. In CMML, there are increased numbers of monocytes and immature blood cells (blasts) in the peripheral blood and bone marrow, as well as abnormal looking cells (dysplasia) in at least one type of blood cell. CMML shows characteristics of a myelodysplastic syndrome (MDS); a disorder that produces abnormal looking blood cells, and a myeloproliferative disorder (MPD); a disorder characterised by the overproduction of blood cells. For this reason CMML was reclassified as a MDS/MPN overlap disorder in 2002. For a diagnosis of CMML, the World Health Organization (WHO) states that the blood monocyte count must be >1x109/L, no Philadelphia chromosome or mutations in the PDGFRA or PDGFRB gene should be present, the blast count must be <20% and dysplasia of at least one lineage of myeloid blood cell should be present. Azacitidine is a drug used to treat CMML and is approved by the Food and Drug Administration (FDA) and the European Medicines Agency. Stem cell transplant is also used to treat CMML, and involves the transplantation of donor haematopoietic stem cells into the recipient. Blood transfusion and erythropoietin are used to treat disease associated anaemia. One of the most common signs of CMML is splenomegaly, found in approximately half of cases. Other less frequent signs and symptoms consist of anaemia, fever, weight loss, night sweats, infection, bleeding, synovitis, lymphadenopathy, skin rashes, pleural effusion, pericardial effusion and peritoneal effusion. Although the cause of CMML is unknown, environmental carcinogens, ionising radiation and cytotoxic agents may have a role in causing disease. Approximately one third of cases of MDS with a monocyte count of >10% and <1x109/L will progress to CMML. With a high rate of Ras mutation in CMML, deregulation of this signalling pathway has been linked to the pathogenesis of the disease. Tumour necrosis factor, GM-CSF, interleukin-3, interleukin-4, interleukin-6, and interleukin-10 may have a role in hyperproliferative CMML cells. These cytokines can stimulate the growth of CMML in vitro. Hypermethylation of cytosine residues (usually in the promoter regions of genes) occurs in many malignancies to regulate gene expression. One commonly hypermethylated gene in CMML is p15INK4b, a gene involved in cell cycle regulation. Clonal genetic abnormalities are common in CMML but they are not specific for diagnosis of the disease. The most common found are the 8+, −7/del (7q) and structural 12p abnormalities. KRAS and NRAS are mutated in 25–40% of the cases of CMML. The Jak2 V617F mutation is found in 10% of cases. Mutations in transcription factors such as RUNX1, CEBPA, NPM1 and WT1 have been found in up to 30% of cases. Mutations of CBL are found in approximately 5–18% of cases. Mutations in the TET2 gene are found in approximately 40–50% of CMML. Inactivating mutations in one of the two parental GATA2 genes lead to a reduction, i.e. a haploinsufficiency, in the cellular levels of the gene's product, the GATA2 transcription factor, and thereby to a rare autosomal dominant genetic disease, GATA2 deficiency. This disease is associated with a highly variable set of disorders including the myelodysplastic syndrome, acute myeloid leukemia, and CMML. GATA2-deficiency-induced CMML, like other types of CMML, is commonly preceded by monocytosis. Blood films display a range of abnormalities. A monocyte count of >1x109/L is essential for a diagnosis of CMML. 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 CMML with eosinophilia); and spherocytosis (in cases of DCT (direct Coombs test) 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 CMML 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 CMML 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.