Adult myeloid leukaemias pathogenesis, clinical features and classification

Leukaemia is a cancer of the bone marrow and blood characterised by abnormal differentiation of haematopoietic stem cells and subsequent overproliferation of blood cells that cannot properly mature. Myeloid leukaemias (also termed myelogenous or granulocytic leukaemias) usually involve the overproduction of immature granulocytic white blood cells, known as blasts (in contrast to lymphoblastic leukaemias, which affect lymphocyte proliferation). The immature granulocytes do not function like mature, healthy white blood cells; they also overcrowd the bone marrow, preventing normal production of red blood cells and platelets. (Some rarer forms of myeloid leukaemia involve the overproliferation of immature red blood cells or platelets.) This article focuses on acute myeloid leukaemia (AML) and chronic myeloid leukaemia (CML), as well as the myelodysplastic syndromes (referred to as MDS). Although MDS is not classified as a leukaemia, it may be considered to be a pre-leukaemic condition. MDS is a bone marrow stem cell disorder that results in ineffective or disordered myeloid cell formation; it causes progressive bone marrow failure and leads to AML in 30% of cases. During recent years, significant progress has been made in understanding the development of these diseases at a molecular level; this has led to important advances in risk stratification and treatment strategies. Treatment is discussed in an accompanying article (p122).