Aetiology

Unknown. Predisposing factors are ionizing radiation (AML is more common) and congenital predisposition in Down's (20-fold in childhood), Bloom's, Klinefelter's and Fanconi's syndromes. Chemicals, pollution, viruses, urban/rural population movements, father's radiation exposure, radon levels and proximity to power lines have all been postulated.

Morphological Classification (French-American-British, FAB)

L1 Small monomorphic type—small homogeneous blasts, single inconspicuous nucleolus, regular nuclear outline; commonest subtype.

L2 Large heterogeneous type—larger blasts, more pleomorphic and multinucleolate, irregular frequently clefted nuclei with conspicuous nucleoli.

L3 Burkitt cell type—large homogeneous blasts, abundant strongly basophilic cytoplasm with vacuoles; associated with B-cell phenotype.

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