Leukaemia (acute)

Acute leukaemia is a malignant clonal expansion of a haemopoietic stem cell. Abnormal white cells accumulate in the bone marrow, gradually replacing normal haemopoietic cells. The result is bone marrow failure and the spilling over of abnormal cells into the peripheral blood. Other tissues may be infiltrated by some types of acute leukaemia.

The aetiology of a case of acute leukaemia is usually not apparent although various environmental and congenital factors have been implicated.

Two main types of acute leukaemia are recognised:

• lymphoblastic:
  • accounts for 20% of all acute leukaemias
  • accounts for 80% of childhood leukaemia
  • peak incidence at age 4 years
    
    
• myeloid:
  • accounts for 80% of acute leukaemias
  • seen mostly in adults
  • peak incidence between 15 and 39 years

Rarely, biphenotypic or mixed leukaemias with features of both lineages are seen.