Epidemiology and pathogenesis
Leukaemias are categorised by cell lineage into four broad groups. In acute lymphoblastic leukaemia (ALL), 60% of cases are in children, with a peak incidence in the first 5 years of life, and drop until age 60, when a second peak emerges. In comparison, acute myeloid leukaemia (AML) is less common in children (20%) but is more common in those over the age of 60. The incidence of both AML and ALL is slightly higher in males than females.
In chronic myeloid leukaemia (CML), the median age at presentation is 50–60 years but is seen in all age groups. Chronic lymphoid leukaemia (CLL) is the most common leukaemia in adults in Western Europe, accounting for 25% of all leukaemias.
Leukaemia arises from a monoclonal origin where cellular clones have an advantage over normal haematological cells. More than 90% of CML cases and a subset of ALL are associated with a reciprocal translocation between chromosomes 9 and 22, which creates a fusion gene from a juxtaposition of the BCR and ABL genes, manifesting as the Philadelphia chromosome.
There is an increased incidence of AML and myelodysplasia seen in persons with prolonged exposure to benzene and petroleum products. Prior chemotherapy with alkylating agents (e.g. cyclophosphamide, melphalan) has been associated with the development of AML, usually within 3–5 years of exposure and often preceded by a myelodysplastic phase. An increased incidence of AML is associated with Down syndrome, Bloom syndrome, Fanconi anaemia and ataxia-telangiectasia. AML arising from myelodysplastic syndromes is often the most resistant to treatment and has a worse prognosis.
Clinical presentation
Leukaemia manifests with symptoms related to its impact on normal haematopoiesis, such as easy fatigability, bruising, bleeding from mucosal surfaces, fever and infection. Patients with very high white cell counts may develop hyperviscosity syndrome, presenting with priapism, tinnitus, stupor, retinal haemorrhages and CVA.
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