Mast cell leukemia (MCL) is the leukemic variant of systemic mastocytosis. Mastocytosis is a heterogeneous disorder characterized by an accumulation of mast cells due to clonal proliferation. It is broadly categorized into three variants: systemic mastocytosis, cutaneous mastocytosis, and mast cell sarcoma.

Mast cell leukemia is a rare and aggressive disease in which ≥20% of bone marrow aspirate smear is composed of abnormal mast cells. Peripheral blood can show varying numbers of mast cells; however, most cases of MCL present as the "aleukemic" variant with fewer than 10% circulating mast cells.

Signs and symptoms include weight loss, anemia, and fatigue, and may include flushing, fever, malaise, diarrhea, tachycardia, and loss of appetite; however, some patients are asymptomatic. Skin findings / rash may be present if the condition evolves from systemic mastocytosis; otherwise, they are typically absent (unlike other forms of mastocytosis). Hepatosplenomegaly is common while fewer patients present with lymphadenopathy and/or skin changes.

Recently, MCL has been divided into a chronic form (with no organ damage present) and a more aggressive acute form (with organ damage present). MCL can arise de novo (majority of cases) or secondary to a systemic mastocytosis. Patients may present at any age; however, the median age of diagnosis is 52 years with a slight female predominance.

Survival with the acute form is poor, with a median survival time of 6 months.

Related topics: Urticaria pigmentosa, Mastocytoma, Diffuse cutaneous mastocytosis