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Clinical features and diagnosis of hairy cell leukemia

Martin S Tallman, MD
Jon C Aster, MD
Section Editor
Richard A Larson, MD
Deputy Editor
Rebecca F Connor, MD


Hairy cell leukemia (HCL) is an uncommon chronic B cell lymphoproliferative disorder (lymphoid neoplasm) characterized by the accumulation of small mature B cell lymphoid cells with abundant cytoplasm and "hairy" projections within the peripheral blood, bone marrow, and splenic red pulp. This typically results in splenomegaly and a variable reduction in the production of normal red blood cells, platelets, mature granulocytes, and monocytes. The increased production of malignant cells, along with a reduction in these mature elements, results in a variety of systemic consequences, including splenomegaly, anemia, bleeding, and an increased risk of infection.

The clinical features and diagnosis of HCL will be reviewed here; treatment of this disorder is discussed separately. (See "Treatment of hairy cell leukemia".)


The pathogenesis of HCL is incompletely understood. Most cases of HCL are postulated to arise from a late, activated memory B cell that acquires a BRAF V600E gene mutation. The resultant aberrant activation of the RAF-MEK-ERK signaling pathway leads to a distinct phenotype and enhanced cell survival. (See 'BRAF mutations' below.)

Exposures to ionizing radiation, pesticides, and farming have been mentioned as possible causes [1-3]. Exposure to solvents, cigarette smoke, alcohol consumption, and obesity do not appear to be risk factors [1,4,5]. A number of familial cases have been described, with family members sharing the same HLA haplotype [6,7].

Cell of origin — HCL is postulated to arise from a late, activated memory B cell exhibiting preplasma cell or postgerminal center features [8,9]. The malignant cell in HCL has the following features:

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Literature review current through: Nov 2017. | This topic last updated: Nov 15, 2017.
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