Lymphoma and plasma cell neoplasms
B cell lymphoma subtypes
Hairy cell leukemia

Topic Completed: 1 February 2011

Minor changes: 28 May 2020

Copyright: 2001-2020,, Inc.

PubMed Search: hairy cell leukemia lymphoma

Nikhil Sangle, M.D.
Page views in 2019: 9,560
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Cite this page: Sangle N. Hairy cell leukemia. website. Accessed July 4th, 2020.
Definition / general
  • Rare chronic leukemia that commonly presents with massive splenomegaly, with tumor cells containing hair-like projections
  • Formerly known as leukemic reticuloendotheliosis
Clinical features
  • Mean age 52 years, range 20 - 80 years; 80% men
  • Commonly presents with massive splenomegaly with obliteration of white pulp and involvement of red pulp, pancytopenia (50%), marrow fibrosis, monocytopenia, infections in 1/3; frequently atypical mycobacterial infections with weakness and weight loss; minimal lymphadenopathy (eMedicine)
  • Bone marrow aspiration biopsies unsuccessful ("dry tap") in 30 - 50% due to marrow fibrosis
  • Excellent prognosis, with near normal life expectancy with appropriate treatment
  • Many patients who achieve a complete remission by morphologic criteria have minimal residual disease demonstrable by flow cytometry or immunohistochemistry, and may be at higher risk for earlier relapse (Blood 2010;115:21)
Case reports
Microscopic (histologic) description
  • Tumor cells are larger than small lymphocytes, modest pale blue agranular cytoplasm with circumferential threadlike extensions seen with phase contrast microscope, round or indented/folded (oval) nuclei, no distinct nucleoli
  • Residual follicles often present
  • Cells line pseudosinuses
  • Blood lakes often present

Bone Marrow:
  • Diffuse or focal involvement with irregular, poorly demarcated infiltrates
  • Cells may be loosely spaced
  • Hairy cell is 10 - 14 microns with abundant, clear to lightly basophic or eosinophilic cytoplasm with surface circumferential delicate and broad projections
  • May have cytoplasmic vacuoles and azurophilic granules
  • Oval / folded / indented nuclei with variable chromatin and no prominent nucleoli
  • May be perinuclear halo in formalin fixed tissue due to abundant cytoplasm
  • Prominent cell borders ("fried egg appearance") with formalin fixation
  • Marked marrow fibrosis and increased mast cells are common
  • No / rare mitotic figures

    Stromal variant: leukemic cells are spindled
  • Microscopic (histologic) images

    Case of the Week #95:

    Cecal lesion from Case of the Week #95: H&E and DBA.44


    Images hosted on other servers:

    Bone marrow biopsy - increased reticulin fibrosis

    Bone marrow trephine biopsy (figures A - F)

    Post treatment bone
    marrow with minimal
    residual disease: H&E
    and DBA.44+ (figure 1B)


    Fig. 1: large lymphocytes with abundant cytoplasm,
    eccentric nuclei, often cytoplasmic projections; Fig. 2: TRAP+;
    Fig. 3: hypercellular bone marrow with monotonous "fried egg"
    lymphocytes with abundant cytoplasm

    Cytology description
    • Small / intermediate size cells with moderate pale gray cytoplasm, cells have circumferential hair-like and short, blunt cytoplasmic projections, round / oval nuclei with smooth nuclear borders, stippled chromatin, occasional nucleoli (Cytojournal 2006;3:1)
    Cytology images

    Images hosted on other servers:

    Peripheral blood

    Lymph node aspirate

    Bone marrow aspirates

    Peripheral smear description
    • Monocytopenia, leukopenia, often no / rare leukemic cells; 5 - 10% have WBC > 10 billion/L, usually due to tumor cells
    Positive stains
    Negative stains
    Differential diagnosis
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