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

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General Information About Hairy Cell Leukemia

Prognostic Factors

Hairy cell leukemia is an indolent, low-grade, B-cell lymphoma usually characterized by the following:

  • Circulating B cells with cytoplasmic projections ("hairy" appearance).
  • Splenomegaly.
  • Absent lymphadenopathy.
  • Pancytopenia.
  • Monocytopenia.

Diagnosis

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.

References:

  1. 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.
  2. Naik RR, Saven A: My treatment approach to hairy cell leukemia. Mayo Clin Proc 87 (1): 67-76, 2012.

Stage Information for Hairy Cell Leukemia

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.[1]

References:

  1. Grever MR, Abdel-Wahab O, Andritsos LA, et al.: Consensus guidelines for the diagnosis and management of patients with classic hairy cell leukemia. Blood 129 (5): 553-560, 2017.

Treatment Option Overview for Hairy Cell Leukemia

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.[4] The adapted treatment guidelines, published in 2021, are based primarily on anecdotal experience and expert opinion.[5][Level of evidence: 3iiiDiv] The adapted treatment guidelines can be summarized as follows:

  1. Consider watchful waiting when feasible; asymptomatic patients with noncritical levels of pancytopenia can be monitored closely.
  2. Avoid using cladribine, with or without rituximab,[3] and pentostatin because of the risk of serious and prolonged immunosuppression.
  3. Consider using BRAF inhibitors such as vemurafenib, dabrafenib, or encorafenib.[6,7,8,9] Most patients with hairy cell leukemia are BRAF mutation-positive, but this should be verified by flow cytometry. There is extensive experience, mostly with vemurafenib in the relapsed setting, but there is no U.S. Food and Drug Administration (FDA) approval for the use of this oral agent in patients with hairy cell leukemia.
  4. Consider using rituximab alone intravenously for 4 to 8 weeks or in combination with a BRAF inhibitor.[10] Anti-CD20 monoclonal antibodies can impair future vaccine response, but do not affect immunity from prior vaccination.
  5. Interferon use is well established, and avoids serious neutropenia or vaccine unresponsiveness.[11,12] Ropeginterferon alfa-2B-njf is the best available preparation, but is not FDA approved for hairy cell leukemia.
  6. In patients with relapsed disease, the previously mentioned options are available, along with ibrutinib, the BTK inhibitor, and moxetumomab pasudotox-tdfk, the anti-CD22 recombinant immunotoxin.[13,14]

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.

References:

  1. Rosenberg JD, Burian C, Waalen J, et al.: Clinical characteristics and long-term outcome of young hairy cell leukemia patients treated with cladribine: a single-institution series. Blood 123 (2): 177-83, 2014.
  2. Saven A, Burian C, Adusumalli J, et al.: Filgrastim for cladribine-induced neutropenic fever in patients with hairy cell leukemia. Blood 93 (8): 2471-7, 1999.
  3. Chihara D, Arons E, Stetler-Stevenson M, et al.: Randomized Phase II Study of First-Line Cladribine With Concurrent or Delayed Rituximab in Patients With Hairy Cell Leukemia. J Clin Oncol 38 (14): 1527-1538, 2020.
  4. Grever MR, Abdel-Wahab O, Andritsos LA, et al.: Consensus guidelines for the diagnosis and management of patients with classic hairy cell leukemia. Blood 129 (5): 553-560, 2017.
  5. Grever M, Andritsos L, Banerji V, et al.: Hairy cell leukemia and COVID-19 adaptation of treatment guidelines. Leukemia 35 (7): 1864-1872, 2021.
  6. Tiacci E, Park JH, De Carolis L, et al.: Targeting Mutant BRAF in Relapsed or Refractory Hairy-Cell Leukemia. N Engl J Med 373 (18): 1733-47, 2015.
  7. Dietrich S, Pircher A, Endris V, et al.: BRAF inhibition in hairy cell leukemia with low-dose vemurafenib. Blood 127 (23): 2847-55, 2016.
  8. Falini B, Tiacci E: New treatment options in hairy cell leukemia with focus on BRAF inhibitors. Hematol Oncol 37 (Suppl 1): 30-37, 2019.
  9. Tiacci E, De Carolis L, Simonetti E, et al.: Vemurafenib plus Rituximab in Refractory or Relapsed Hairy-Cell Leukemia. N Engl J Med 384 (19): 1810-1823, 2021.
  10. Angelopoulou MK, Pangalis GA, Sachanas S, et al.: Outcome and toxicity in relapsed hairy cell leukemia patients treated with rituximab. Leuk Lymphoma 49 (9): 1817-20, 2008.
  11. Golomb HM, Ratain MJ, Fefer A, et al.: Randomized study of the duration of treatment with interferon alfa-2B in patients with hairy cell leukemia. J Natl Cancer Inst 80 (5): 369-73, 1988.
  12. Capnist G, Federico M, Chisesi T, et al.: Long term results of interferon treatment in hairy cell leukemia. Italian Cooperative Group of Hairy Cell Leukemia (ICGHCL). Leuk Lymphoma 14 (5-6): 457-64, 1994.
  13. Jones J, Andritsos L, Kreitman RJ: Efficacy and safety of the Bruton tyrosine kinase inhibitor ibrutinib in patients with hairy cell leukemia: stage 1 results of a phase 2 study. [Abstract] Blood 128 (22): A-1215, 2016.
  14. Kreitman RJ, Dearden C, Zinzani PL, et al.: Moxetumomab pasudotox in relapsed/refractory hairy cell leukemia. Leukemia 32 (8): 1768-1777, 2018.

Treatment of Hairy Cell Leukemia

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:

  1. Watchful waiting, if feasible.
  2. Rituximab.
  3. Vemurafenib (or other BRAF inhibitors) with or without rituximab.
  4. Recombinant interferon alfa.
  5. Ibrutinib.
  6. Moxetumomab pasudotox-tdfk.
  7. Cladribine with or without rituximab.
  8. Pentostatin.
  9. Re-treatment with cladribine or pentostatin.
  10. Splenectomy.

Rituximab

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.[6][Level of evidence: 3iiiDiv] Vemurafenib can be given in combination with rituximab.

Evidence (vemurafenib with or without rituximab):

  1. Three phase II, multicenter studies in the United States and Italy evaluated the BRAF inhibitor vemurafenib, given orally alone for 4 months or orally for 2 months with rituximab infused in eight doses over 18 weeks for patients with relapsed or refractory hairy cell leukemia.[7,8,9]
    • After a median follow-up of 23 months, using vemurafenib alone, the overall response rate for 50 patients was 98%, the complete response rate was 38%, and the median treatment-free survival was 25 months and 18 months in the two studies.[7,8][Level of Evidence: 3iiiDiv]
    • After a median follow-up of 37 months, for the 30 patients treated with vemurafenib plus rituximab, the complete response rate was 87%. The progression-free survival (PFS) rate was 78% at 37 months, and 65% of patients were cleared of minimal residual disease.[9][Level of Evidence: 3iiiDiv]

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.[10] Remission can be prolonged with a low-dose maintenance regimen.[11]

Evidence (recombinant interferon alfa):

  1. A randomized comparison of pentostatin and recombinant interferon alfa demonstrated significantly higher and more durable responses to pentostatin.[12]

Ibrutinib

Evidence (ibrutinib):

  1. In a phase II study, with a median follow-up of 42 months, 37 patients with refractory hairy cell leukemia had a 54% response rate to ibrutinib, with an estimated 36-month PFS rate of 73% and an overall survival (OS) rate of 85%.[13][Level of evidence: 3iiiDiv]

Moxetumomab Pasudotox-tdfk

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):

  1. Moxetumomab pasudotox-tdfk was given to 80 patients who were previously treated with at least two regimens.[18][Level of evidence: 3iiiDiv]
    • In a phase II trial, 75% of patients responded and 30% had a complete response.

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):

  1. A retrospective review included 83 patients, aged 40 years and younger.[25]
    • The median time to first relapse was 54 months for all responders and the median OS was 21 years from diagnosis.
    • This drug may cause fever and immunosuppression; documented infection was found in 33% of treated patients.
  2. In a retrospective study of patients with cladribine-associated neutropenic fever, filgrastim (G-CSF) did not demonstrate a decrease in the percentage of febrile patients, number of febrile days, or frequency of hospital admissions to receive antibiotics.[26] There is a potential increased risk of developing second malignancies with this agent.
  3. In a phase II study, 68 patients with previously untreated hairy cell leukemia were randomly assigned to receive cladribine 0.15 mg/kg intravenously on days 1 to 5, with eight weekly doses of rituximab concurrently (starting on day 1) or after 6 months if still positive with minimal residual disease (MRD) testing.[27]
    • With a median follow-up of 96 months, 94% of patients who received concurrent therapy were MRD-free, compared with 12% of patients who received delayed therapy.[27][Level of evidence: 3iiiDiv]
    • Concurrent therapy resulted in more need for platelet transfusions, but also higher neutrophil and platelet counts after 1 month.

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

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.

Evidence (pentostatin):

  1. In two trials with 9-year median follow-ups, relapse-free survival rates ranged from 56% to 67%.[29,30]
    • Side effects included fever, immunosuppression, cytopenias, and renal dysfunction.
  2. A randomized comparison of pentostatin and recombinant interferon alpha-2a demonstrated higher and more durable responses to pentostatin.[12]

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

Splenectomy will partially or completely normalize the peripheral blood in most patients with hairy cell leukemia.[35] 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.

References:

  1. Gerrie AS, Zypchen LN, Connors JM: Fludarabine and rituximab for relapsed or refractory hairy cell leukemia. Blood 119 (9): 1988-91, 2012.
  2. Hagberg H, Lundholm L: Rituximab, a chimaeric anti-CD20 monoclonal antibody, in the treatment of hairy cell leukaemia. Br J Haematol 115 (3): 609-11, 2001.
  3. Lauria F, Lenoci M, Annino L, et al.: Efficacy of anti-CD20 monoclonal antibodies (Mabthera) in patients with progressed hairy cell leukemia. Haematologica 86 (10): 1046-50, 2001.
  4. Thomas DA, O'Brien S, Bueso-Ramos C, et al.: Rituximab in relapsed or refractory hairy cell leukemia. Blood 102 (12): 3906-11, 2003.
  5. Angelopoulou MK, Pangalis GA, Sachanas S, et al.: Outcome and toxicity in relapsed hairy cell leukemia patients treated with rituximab. Leuk Lymphoma 49 (9): 1817-20, 2008.
  6. Pettirossi V, Santi A, Imperi E, et al.: BRAF inhibitors reverse the unique molecular signature and phenotype of hairy cell leukemia and exert potent antileukemic activity. Blood 125 (8): 1207-16, 2015.
  7. Tiacci E, Park JH, De Carolis L, et al.: Targeting Mutant BRAF in Relapsed or Refractory Hairy-Cell Leukemia. N Engl J Med 373 (18): 1733-47, 2015.
  8. Dietrich S, Pircher A, Endris V, et al.: BRAF inhibition in hairy cell leukemia with low-dose vemurafenib. Blood 127 (23): 2847-55, 2016.
  9. Tiacci E, De Carolis L, Simonetti E, et al.: Vemurafenib plus Rituximab in Refractory or Relapsed Hairy-Cell Leukemia. N Engl J Med 384 (19): 1810-1823, 2021.
  10. Golomb HM, Ratain MJ, Fefer A, et al.: Randomized study of the duration of treatment with interferon alfa-2B in patients with hairy cell leukemia. J Natl Cancer Inst 80 (5): 369-73, 1988.
  11. Capnist G, Federico M, Chisesi T, et al.: Long term results of interferon treatment in hairy cell leukemia. Italian Cooperative Group of Hairy Cell Leukemia (ICGHCL). Leuk Lymphoma 14 (5-6): 457-64, 1994.
  12. Grever M, Kopecky K, Foucar MK, et al.: Randomized comparison of pentostatin versus interferon alfa-2a in previously untreated patients with hairy cell leukemia: an intergroup study. J Clin Oncol 13 (4): 974-82, 1995.
  13. Rogers KA, Andritsos LA, Wei L, et al.: Phase 2 study of ibrutinib in classic and variant hairy cell leukemia. Blood 137 (25): 3473-3483, 2021.
  14. Kreitman RJ, Tallman MS, Robak T, et al.: Minimal residual hairy cell leukemia eradication with moxetumomab pasudotox: phase 1 results and long-term follow-up. Blood 131 (21): 2331-2334, 2018.
  15. Kreitman RJ, Wilson WH, White JD, et al.: Phase I trial of recombinant immunotoxin anti-Tac(Fv)-PE38 (LMB-2) in patients with hematologic malignancies. J Clin Oncol 18 (8): 1622-36, 2000.
  16. Kreitman RJ, Stetler-Stevenson M, Margulies I, et al.: Phase II trial of recombinant immunotoxin RFB4(dsFv)-PE38 (BL22) in patients with hairy cell leukemia. J Clin Oncol 27 (18): 2983-90, 2009.
  17. Kreitman RJ, Tallman MS, Robak T, et al.: Phase I trial of anti-CD22 recombinant immunotoxin moxetumomab pasudotox (CAT-8015 or HA22) in patients with hairy cell leukemia. J Clin Oncol 30 (15): 1822-8, 2012.
  18. Kreitman RJ, Dearden C, Zinzani PL, et al.: Moxetumomab pasudotox in relapsed/refractory hairy cell leukemia. Leukemia 32 (8): 1768-1777, 2018.
  19. Robak T, Błasińska-Morawiec M, Krykowski E, et al.: 2-chlorodeoxyadenosine (2-CdA) in 2-hour versus 24-hour intravenous infusion in the treatment of patients with hairy cell leukemia. Leuk Lymphoma 22 (1-2): 107-11, 1996.
  20. Robak T, Jamroziak K, Gora-Tybor J, et al.: Cladribine in a weekly versus daily schedule for untreated active hairy cell leukemia: final report from the Polish Adult Leukemia Group (PALG) of a prospective, randomized, multicenter trial. Blood 109 (9): 3672-5, 2007.
  21. Zenhäusern R, Schmitz SF, Solenthaler M, et al.: Randomized trial of daily versus weekly administration of 2-chlorodeoxyadenosine in patients with hairy cell leukemia: a multicenter phase III trial (SAKK 32/98). Leuk Lymphoma 50 (9): 1501-11, 2009.
  22. Jehn U, Bartl R, Dietzfelbinger H, et al.: An update: 12-year follow-up of patients with hairy cell leukemia following treatment with 2-chlorodeoxyadenosine. Leukemia 18 (9): 1476-81, 2004.
  23. Chadha P, Rademaker AW, Mendiratta P, et al.: Treatment of hairy cell leukemia with 2-chlorodeoxyadenosine (2-CdA): long-term follow-up of the Northwestern University experience. Blood 106 (1): 241-6, 2005.
  24. Else M, Dearden CE, Matutes E, et al.: Long-term follow-up of 233 patients with hairy cell leukaemia, treated initially with pentostatin or cladribine, at a median of 16 years from diagnosis. Br J Haematol 145 (6): 733-40, 2009.
  25. Rosenberg JD, Burian C, Waalen J, et al.: Clinical characteristics and long-term outcome of young hairy cell leukemia patients treated with cladribine: a single-institution series. Blood 123 (2): 177-83, 2014.
  26. Saven A, Burian C, Adusumalli J, et al.: Filgrastim for cladribine-induced neutropenic fever in patients with hairy cell leukemia. Blood 93 (8): 2471-7, 1999.
  27. Chihara D, Arons E, Stetler-Stevenson M, et al.: Randomized Phase II Study of First-Line Cladribine With Concurrent or Delayed Rituximab in Patients With Hairy Cell Leukemia. J Clin Oncol 38 (14): 1527-1538, 2020.
  28. Ribeiro P, Bouaffia F, Peaud PY, et al.: Long term outcome of patients with hairy cell leukemia treated with pentostatin. Cancer 85 (1): 65-71, 1999.
  29. Johnston JB, Eisenhauer E, Wainman N, et al.: Long-term outcome following treatment of hairy cell leukemia with pentostatin (Nipent): a National Cancer Institute of Canada study. Semin Oncol 27 (2 Suppl 5): 32-6, 2000.
  30. Flinn IW, Kopecky KJ, Foucar MK, et al.: Long-term follow-up of remission duration, mortality, and second malignancies in hairy cell leukemia patients treated with pentostatin. Blood 96 (9): 2981-6, 2000.
  31. Hoffman MA, Janson D, Rose E, et al.: Treatment of hairy-cell leukemia with cladribine: response, toxicity, and long-term follow-up. J Clin Oncol 15 (3): 1138-42, 1997.
  32. Goodman GR, Burian C, Koziol JA, et al.: Extended follow-up of patients with hairy cell leukemia after treatment with cladribine. J Clin Oncol 21 (5): 891-6, 2003.
  33. Zinzani PL, Magagnoli M, Bendandi M, et al.: Long-term follow-up of hairy cell leukemia patients treated with 2-chlorodeoxyadenosine. Haematologica 85 (9): 922-5, 2000.
  34. Gidron A, Tallman MS: 2-CdA in the treatment of hairy cell leukemia: a review of long-term follow-up. Leuk Lymphoma 47 (11): 2301-7, 2006.
  35. Golomb HM, Vardiman JW: Response to splenectomy in 65 patients with hairy cell leukemia: an evaluation of spleen weight and bone marrow involvement. Blood 61 (2): 349-52, 1983.

Changes to This Summary (01 / 14 / 2022)

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.

About This PDQ Summary

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:

  • be discussed at a meeting,
  • be cited with text, or
  • replace or update an existing article that is already cited.

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:

  • Eric J. Seifter, MD (Johns Hopkins University)

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.

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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.

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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]

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Last Revised: 2022-01-14