Leukaemia
A group of malignant clonal disorders of blood-forming cells, classified along two axes that decide everything else: cell lineage (myeloid or lymphoid) and tempo (acute, a maturation arrest that fills the marrow with blasts over weeks, or chronic, a slow expansion of maturing cells over years).
Definition
Leukaemia is a clonal haematopoietic malignancy classified by lineage and maturation tempo. Acute entities are blast-driven and rapidly progressive; chronic entities retain maturation and often follow a slower course. Definitive classification requires integrated morphology, immunophenotyping and genetic testing.
First principles
Two questions define every leukaemia: which lineage, and how fast
All leukaemias are clonal malignancies of haematopoietic cells, but naming one requires answering two independent questions. First, lineage: is the clone myeloid (the granulocyte, monocyte, red cell and platelet line) or lymphoid (B and T cells)? Second, tempo: is it acute (a block in maturation, so immature blasts accumulate) or chronic (maturation is preserved, so more mature cells expand slowly)? Crossing these gives the four core diseases: AML, ALL, CML and CLL. Lineage is settled by immunophenotyping, tempo by the cell's maturity on the film and marrow.
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