Hairy Cell Leukemia Treatment (PDQ®): Treatment - Health Professional Information [NCI]

General Information About Hairy Cell Leukemia

Incidence and Mortality

Hairy cell leukemia is an indolent, low-grade, B-cell lymphoid malignancy. It is rare, with only 1,200 to 1,300 new cases annually in the United States.[1]

Clinical Presentation

Hairy cell leukemia usually presents with:

• Splenomegaly.
• Varying degrees of leukopenia (occasionally leukocytosis).
• Pancytopenia.
• Monocytopenia.
• Bone marrow infiltration by atypical cells with prominent cytoplasmic projections (i.e., hairy cells).

Lymphadenopathy is absent, except with multiply recurrent progressive disease.

Diagnostic Evaluation

The following tests and procedures may be used to diagnose hairy cell leukemia:

• Flow cytometry.
• Bone marrow aspiration and biopsy.
• Immunophenotyping.
• Cytogenetic analysis.
• BRAF gene testing.
• Computed tomography scan.

The bone marrow is usually fibrotic and is not easily aspirated. It has circulating B cells with cytoplasmic projections (hairy appearance). Although a bone marrow biopsy may be required to enroll in a clinical trial, the hairy cell leukemia diagnosis can usually be made by flow cytometry.

In addition to the B-cell antigens CD19, CD20 (very high levels), and CD22, the cells coexpress CD11c, CD25, and CD103. The BRAF V600E pathogenic variant is a hairy cell leukemia–defining genetic feature that can aid in diagnosis.[2,3]

There is a variation of hairy cell leukemia (HCL-v) which accounts for 10% of cases. HCL-v is distinguished clinically by an elevated white blood cell count (15–50 × 10⁹ /L) and aberrant markers, including variable (instead of bright) CD103 and the absence of CD23, CD25, CD12, and CD43.[4,5] HCL-v cells also lack BRAF variants. Patients with HCL-v have more aggressive clinical courses, reduced responses to purine nucleoside analogue-based therapy, and shorter durations of response.[5]

The depth of a complete remission can be evaluated with measurable residual disease (MRD) by testing for a BRAF variant or an immunoglobulin heavy chain gene rearrangement. However, the usefulness of altering therapeutic choices with MRD remains unclear and requires further evaluation.[6]

References:

1. Falini B, Tiacci E: Hairy-Cell Leukemia. N Engl J Med 391 (14): 1328-1341, 2024.
2. Tiacci E, Schiavoni G, Forconi F, et al.: Simple genetic diagnosis of hairy cell leukemia by sensitive detection of the BRAF-V600E mutation. Blood 119 (1): 192-5, 2012.
3. Naik RR, Saven A: My treatment approach to hairy cell leukemia. Mayo Clin Proc 87 (1): 67-76, 2012.
4. Jones G, Parry-Jones N, Wilkins B, et al.: Revised guidelines for the diagnosis and management of hairy cell leukaemia and hairy cell leukaemia variant*. Br J Haematol 156 (2): 186-95, 2012.
5. Troussard X, Grever MR: The revised guidelines for the diagnosis and management of hairy cell leukaemia and the hairy cell leukaemia variant. Br J Haematol 193 (1): 11-14, 2021.
6. Ravandi F, Kreitman RJ, Tiacci E, et al.: Consensus opinion from an international group of experts on measurable residual disease in hairy cell leukemia. Blood Cancer J 12 (12): 165, 2022.