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


Definition

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.