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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.
For the purpose of treatment decisions, it is best to consider this disease in the following two broad categories:
Untreated hairy cell leukemia
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. Bone marrow biopsies are, therefore, required for diagnosis and evaluation of the degree of hairy cell infiltration.
Progressive hairy cell leukemia
Progressive hairy cell leukemia, postsplenectomy (or following any systemic therapy) is characterized by progressive bone marrow replacement by hairy cells with pancytopenia refractory to treatment. For patients with advanced hairy cell leukemia treated with cladribine (2-chlorodeoxyadenosine, 2-CdA), pentostatin, or interferon-alpha, the survival rate appears to be more than 85% at 5 years following the initiation of any one of these therapies.[1,2]
The initial therapies of choice are either cladribine (2-chlorodeoxyadenosine, 2-CdA) or pentostatin.[1,2] These drugs have comparable response rates but have not been compared in phase III trials. Cladribine is administered as a one-time continuous infusion or series of subcutaneous injections and is associated with a high rate of febrile neutropenia.[3,4,5,6] Rarely, more than one course of treatment is required to induce a desirable response. Treatment should be discontinued once complete remission or stable partial remission with normalization of peripheral blood counts is reached. The presence of residual disease may be predictive of relapse but does not seem to affect survival.[5,7]
The role of consolidation or maintenance therapy in preventing relapse or progression of the disease following treatment with purine analogs has not been evaluated and remains unproven. Pentostatin is administered intermittently for a longer treatment duration but may result in a lower incidence of febrile complications.[8,9] While most patients remain disease free 10 years after treatment with these purine analogs, no patient has been followed long enough to assess cure.[10,11] Both nucleoside analogs cause profound suppression of CD4 counts, which may last for a year, and a potential increased risk of second malignancies has been reported.[5,12]
A study of 3,104 survivors of hairy cell leukemia from the SEER database showed an increased risk of second cancers (standardized incidence ratio, 1.24; 95% CI, 1.11–1.37), especially for Hodgkin and non-Hodgkin lymphomas. The increased risk for second cancers was seen even in the 2 decades before the introduction of purine nucleosides. With the use of cladribine, an increased risk of second malignancies is possible among patients with hairy cell leukemia (observed to expected ratio of about 1.8 in several series after 6 years).[5,12] Several series using pentostatin did not report an increased risk of second malignancies.[8,10,14] For a few patients, such as those with severe thrombocytopenia, splenectomy might be considered. After splenectomy, 50% of patients will require no additional therapy, and long-term survivors are common. Therapy with interferon-alpha is another treatment option, especially for patients with intercurrent infection.[9,16]
The hairy cell leukemia variant has a distinctive phenotype and typically presents with leukocytosis instead of leukopenia. Patients with this variant have poorer responses to initial cladribine, shorter durations of response, and typically do not respond again to purine analogues after relapse. Combinations of rituximab and purine analogues are under evaluation and further studies are required to define optimal therapies.[18,19]
Untreated Hairy Cell Leukemia
Hairy cell leukemia is a highly treatable disease. Since it is easily controlled, many patients have prolonged survival with 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 blood counts are maintained in an acceptable range.
Progressive Hairy Cell Leukemia
Standard treatment options:
Ongoing trials are studying combinations of cladribine plus the monoclonal antibody rituximab.
Current Clinical Trials
Check for U.S. clinical trials from NCI's list of cancer clinical trials that are now accepting patients with untreated hairy cell leukemia and progressive hairy cell leukemia, initial treatment. The list of clinical trials can be further narrowed by location, drug, intervention, and other criteria.
General information about clinical trials is also available from the NCI Web site.
Cladribine (2-chlorodeoxyadenosine, 2-CdA) and pentostatin are both highly efficacious in the treatment of patients with disease refractory to interferon-alpha.[1,2,3,4] Patients who relapse after the first course of cladribine or pentostatin often respond well to retreatment with the same or another purine analog.[5,6,7,8,9,10,11] Rituximab can induce durable complete remissions with minimal toxic effects in patients with multiple relapsing or refractory disease after purine analog therapy or after interferon.[12,13,14,15][Level of evidence: 3iiiDiv] The lack of subsequent immunosuppression with rituximab has made this treatment a common choice among relapsing patients in the absence of a clinical trial. Combinations of rituximab with either cladribine or pentostatin are effective in achieving complete remission and are under clinical evaluation.[10,16,17] Both anti-CD25 and anti-CD22 recombinant immunotoxins under clinical evaluation can induce complete remissions in patients whose disease is resistant to retreatment with purine analogs or rituximab.[18,19]
Trials (including the ongoing CAT-8015-1001 [NCT00462189] study and NCI-04-C-0014, which is now completed) are in the process of evaluating, or have evaluated, new therapies for this group of patients.
Aggressive, high-dose chemotherapy has been beneficial in some cases, but the associated morbidity and mortality are high. It should not be considered unless other, more frequently effective, therapies have been exhausted.
Check for U.S. clinical trials from NCI's list of cancer clinical trials that are now accepting patients with refractory hairy cell leukemia. The list of clinical trials can be further narrowed by location, drug, intervention, and other criteria.
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.
Editorial changes were made to this section.
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 who care for cancer 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 reviewers for Hairy Cell Leukemia Treatment are:
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Levels of Evidence
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National Cancer Institute: PDQ® Hairy Cell Leukemia Treatment. Bethesda, MD: National Cancer Institute. Date last modified <MM/DD/YYYY>. Available at: http://www.cancer.gov/types/leukemia/hp/hairy-cell-treatment-pdq. Accessed <MM/DD/YYYY>.
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Last Revised: 2015-07-08
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