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WHO Classification of Tumours
Mast cell leukaemia
Tumours of haematopoietic and lymphoid tissues


Mast cell leukaemia (MCL) meets the diagnosic criteria criteria for systemic mastocytosis (SM). Bone marrow biopsy shows a diffuse infiltration, usually compact, by atypical, immature mast cells. Bone marrow aspirate smears show 20% or more mast cells. In typical MCL, mast cells account for 10% or more of peripheral blood white cells.
Rare variant: aleukaemic mast cell leukaemia as above, but <10% of white blood cells are mast cells. Usually without skin lesions.