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This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http://cancer.gov or call 1-800-4-CANCER.
Hairy cell leukemia is an indolent, low-grade, B-cell lymphoma usually characterized by the following:
In addition to the B-cell antigens CD19, CD20, and CD22, the cells coexpress CD11c, CD25, and CD103. The BRAF-V600E mutation is a hairy cell leukemia–defining genetic lesion that can be used diagnostically.[1,2] The decision to treat is based on symptomatic cytopenias, massive splenomegaly, or the presence of other complications. About 10% of all patients will never require therapy.
No generally accepted staging system is useful for both prognosis and therapy.
Untreated hairy cell leukemia is characterized by splenomegaly, varying degrees of leukopenia (occasionally leukocytosis) and/or pancytopenia, and bone marrow infiltration by an atypical cell with prominent cytoplasmic projections (i.e., hairy cells). The bone marrow is usually fibrotic and is not easily aspirated. Although a bone marrow biopsy may be required for enrollment in a clinical trial, the leukemia diagnosis can usually be obtained by flow cytometry.
After the initiation of treatment with cladribine, pentostatin, or recombinant interferon alfa, the survival rate of patients with advanced hairy cell leukemia appears to be higher than 85% after 5 years of follow-up.
Prior to the COVID-19 (SARS-CoV-2) pandemic, the standard initial therapy for patients with hairy cell leukemia was infusion of cladribine daily for 5 days, given with or without eight weekly doses of rituximab.[1,2,3] However, treatment with a purine analogue-based regimen leads to significant and prolonged neutropenia and impairment of T-cell function, both problematic during the pandemic in terms of fighting viral infection and establishing vaccination-induced immunity. The Hairy Cell Leukemia Foundation convened a virtual meeting of 39 experts from around the world to amend 2017 consensus recommendations. The adapted treatment guidelines, published in 2021, are based primarily on anecdotal experience and expert opinion.[Level of evidence: 3iiiDiv] The adapted treatment guidelines can be summarized as follows:
Hairy cell leukemia is rare, with only 600 to 800 new cases annually in the United States. Given the low incidence, these expert recommendations based on anecdotal experience heavily influence the choice of therapeutic options as controlled trials for this indolent leukemia cannot be completed expeditiously.
Hairy cell leukemia is highly treatable but rarely cured. Because it is easily controlled, many patients have prolonged survival with the use of sequential therapies. The decision to treat is based on cytopenias (especially if symptomatic), increasing splenomegaly, indications that the disease is progressing, or the presence of other, usually infectious complications. It is reasonable to offer no therapy if the patient is asymptomatic and if blood counts are maintained in an acceptable range. During the COVID-19 (SARS-CoV-2) pandemic, some options for initial standard therapy, including cladribine or pentostatin, have been replaced in favor of other options with less toxicity, but these options also elicit less-durable responses.
Treatment options for hairy cell leukemia include the following:
Rituximab can induce durable complete remissions with minimal toxic effects in patients with multiple relapsing or refractory disease after purine analogue therapy or after treatment with interferon.[1,2,3,4,5][Level of evidence: 3iiiDiv]
Vemurafenib With or Without Rituximab
The BRAF-V600E mutation occurs in almost 100% of patients with classic-form hairy cell leukemia and almost never in patients with other B-cell lymphomas and leukemias, including hairy cell leukemia variants.[Level of evidence: 3iiiDiv] Vemurafenib can be given in combination with rituximab.
Evidence (vemurafenib with or without rituximab):
Recombinant Interferon Alfa
Recombinant interferon alfa given subcutaneously three times per week for 1 year yields a 10% complete response rate and an 80% overall response rate. The drug frequently produces an influenza-like syndrome early in the course of treatment. Late effects include depression and lethargy. Responding patients who relapse usually react positively to re-treatment with recombinant interferon alfa. Remission can be prolonged with a low-dose maintenance regimen.
Evidence (recombinant interferon alfa):
Moxetumomab pasudotox-tdfk is an anti-CD22 recombinant immunotoxin that the U.S. Food and Drug Administration approved to treat patients with relapsed or refractory disease.[14,15,16,17]
Evidence (moxetumomab pasudotox-tdfk):
Cladribine With or Without Rituximab
Cladribine given intravenously by daily subcutaneous injections, or by 2-hour infusions daily for 5 to 7 days results in a complete response rate of 50% to 80% and an overall response rate of 85% to 95%.[19,20,21][Level of evidence: 3iiiDiv] The response rate was lower in 979 patients treated with the Group C mechanism of the National Cancer Institute (i.e., 50% complete remission rate, 37% partial remission rate). Responses are durable with this short course of therapy, and patients who relapse often respond to re-treatment with cladribine.[22,23,24]
Evidence (cladribine with or without rituximab):
MRD testing in this setting has never been validated as a clinically significant end point. This concept requires further study, but hairy cell leukemia is rare, with only 600 to 800 new cases annually in the United States.
Pentostatin given intravenously every other week for 3 to 6 months produces a 50% to 76% complete response rate and an 80% to 87% overall response rate.[12,28] Complete remissions are of substantial duration.
Re-treatment With Cladribine or Pentostatin
Patients with hairy cell leukemia who relapse after the first course of cladribine or pentostatin often respond well to re-treatment with the same or another purine analogue, especially if relapse occurs after 2 years.[24,28,31,32,33,34][Level of evidence: 3iiiDiv]
Splenectomy will partially or completely normalize the peripheral blood in most patients with hairy cell leukemia. Usually little or no change occurs in the bone marrow after splenectomy, and virtually all patients have progressive disease within 12 to 18 months. Therefore, because a number of more effective alternatives are available, splenectomy plays a decreasing role in the treatment of this disease.
Current Clinical Trials
Use our advanced clinical trial search to find NCI-supported cancer clinical trials that are now enrolling patients. The search can be narrowed by location of the trial, type of treatment, name of the drug, and other criteria. General information about clinical trials is also available.
The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.
This summary was comprehensively reviewed and extensively revised.
This summary is written and maintained by the PDQ Adult Treatment Editorial Board, which is editorially independent of NCI. The summary reflects an independent review of the literature and does not represent a policy statement of NCI or NIH. More information about summary policies and the role of the PDQ Editorial Boards in maintaining the PDQ summaries can be found on the About This PDQ Summary and PDQ® - NCI's Comprehensive Cancer Database pages.
Purpose of This Summary
This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about the treatment of hairy cell leukemia. It is intended as a resource to inform and assist clinicians in the care of their patients. It does not provide formal guidelines or recommendations for making health care decisions.
Reviewers and Updates
This summary is reviewed regularly and updated as necessary by the PDQ Adult Treatment Editorial Board, which is editorially independent of the National Cancer Institute (NCI). The summary reflects an independent review of the literature and does not represent a policy statement of NCI or the National Institutes of Health (NIH).
Board members review recently published articles each month to determine whether an article should:
Changes to the summaries are made through a consensus process in which Board members evaluate the strength of the evidence in the published articles and determine how the article should be included in the summary.
The lead reviewer for Hairy Cell Leukemia Treatment is:
Any comments or questions about the summary content should be submitted to Cancer.gov through the NCI website's Email Us. Do not contact the individual Board Members with questions or comments about the summaries. Board members will not respond to individual inquiries.
Levels of Evidence
Some of the reference citations in this summary are accompanied by a level-of-evidence designation. These designations are intended to help readers assess the strength of the evidence supporting the use of specific interventions or approaches. The PDQ Adult Treatment Editorial Board uses a formal evidence ranking system in developing its level-of-evidence designations.
Permission to Use This Summary
PDQ is a registered trademark. Although the content of PDQ documents can be used freely as text, it cannot be identified as an NCI PDQ cancer information summary unless it is presented in its entirety and is regularly updated. However, an author would be permitted to write a sentence such as "NCI's PDQ cancer information summary about breast cancer prevention states the risks succinctly: [include excerpt from the summary]."
The preferred citation for this PDQ summary is:
PDQ® Adult Treatment Editorial Board. PDQ Hairy Cell Leukemia Treatment. Bethesda, MD: National Cancer Institute. Updated <MM/DD/YYYY>. Available at: https://www.cancer.gov/types/leukemia/hp/hairy-cell-treatment-pdq. Accessed <MM/DD/YYYY>. [PMID: 26389184]
Images in this summary are used with permission of the author(s), artist, and/or publisher for use within the PDQ summaries only. Permission to use images outside the context of PDQ information must be obtained from the owner(s) and cannot be granted by the National Cancer Institute. Information about using the illustrations in this summary, along with many other cancer-related images, is available in Visuals Online, a collection of over 2,000 scientific images.
Based on the strength of the available evidence, treatment options may be described as either "standard" or "under clinical evaluation." These classifications should not be used as a basis for insurance reimbursement determinations. More information on insurance coverage is available on Cancer.gov on the Managing Cancer Care page.
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Last Revised: 2022-01-14
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