11.6 Acute leukaemia
Introduction
The leukaemias are a group of diseases characterised by the clonal proliferation of malignant immature white blood cell precursors. They differ in the lineage and degree of differentiation of cells involved, being broadly divided into two groups: lymphoid and myeloid. These two categories are further subdivided into an acute form that progresses more rapidly than the chronic disease, which is relatively indolent. Preconceptional germ cell and postnatal environmental exposure to electromagnetic radiation and carcinogens may play a role,1–3 with higher risk in children with congenital neutropenia, Down’s syndrome and Fanconi anaemia.4 Previous chemotherapy and radiotherapy are associated with increased risk of a secondary malignancy. Acute lymphoblastic leukaemia (ALL) comprises four-fifths of childhood leukaemia,4 with acute myeloid leukaemia (AML) and chronic myeloid leukaemia (CML) accounting for 15% and 2%.5 Together they account for one-third of all malignancies in children under 15 years old. Although children of all ages are affected, the peak incidence is between 2 and 6 years.
Classification
Leukaemogenesis represents clonal proliferation of white blood cells arrested at various stages of differentiation, lending itself to diagnostic and prognostic classification based on the cell line affected, degree of differentiation, immunophenotyping, cell receptor, cell antigen and chromosomal studies. Classification of leukaemia is complex, with the French–American–British (FAB) categories being useful for AML and immunotyping better suiting ALL.4,5
