LQCL2607 - CMLE - Hairy Cell Leukemia-LQCL2607

LQCL2607 - Educational Activity

Pdf Summary

Hairy cell leukemia (HCL) is a rare, indolent mature B‑cell neoplasm (~2% of lymphoid leukemias) that primarily involves bone marrow, peripheral blood, and spleen, and occurs most often in adults. Patients commonly present with cytopenias—classically pancytopenia with prominent monocytopenia—and may have fatigue, fever, infections, bleeding, night sweats, and left upper quadrant discomfort from splenomegaly; lymphadenopathy is uncommon. Peripheral blood can show few circulating neoplastic cells, making careful smear review important.<br /><br />Morphologically, HCL cells are small to intermediate (about twice a normal lymphocyte), with oval to indented/kidney-shaped nuclei, clumped or slightly loosened chromatin, inconspicuous nucleoli, and variably abundant blue‑gray cytoplasm with fine, circumferential “hairy” cytoplasmic projections. In tissue sections, abundant pale cytoplasm can create a “fried egg” appearance. Bone marrow often shows interstitial infiltration and increased reticulin with frequent “dry tap,” related to fibronectin produced by hairy cells; therefore, trephine biopsy is key for diagnosis.<br /><br />The characteristic immunophenotype includes bright B‑cell markers and surface immunoglobulin (CD19, CD20, CD22), with CD11c (often bright), CD25, CD103, CD123, annexin A1, and CD200; cyclin D1 may be variably/focally positive without CCND1 rearrangement. Molecularly, BRAF p.V600E is present in ~95% of classic HCL and serves as a diagnostic hallmark that helps distinguish HCL from splenic marginal zone lymphoma, splenic diffuse red pulp small B‑cell lymphoma, and HCL variant (which typically lacks BRAF V600E and key markers such as CD25/ANXA1/CD123).<br /><br />HCL is highly treatable but rarely curable. Some asymptomatic patients can be observed. Standard first-line therapy is purine nucleoside analogs; relapsed/refractory disease may benefit from targeted approaches (e.g., BRAF inhibitors ± rituximab, anti‑CD22 immunotoxins). Measurable residual disease after therapy predicts shorter time to relapse. The case described fit classic HCL by morphology, immunophenotype, and BRAF V600E and was treated with cladribine plus rituximab.

Keywords

hairy cell leukemia

B-cell neoplasm

pancytopenia

monocytopenia

splenomegaly

dry tap bone marrow

fried egg appearance

BRAF V600E

immunophenotype CD11c CD25 CD103 CD123 annexin A1

cladribine rituximab