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PubMed This is a summary of 39 peer-reviewed journal articles Updated
Hematology

Introduction to Classic Hairy Cell Leukemia

At a Glance

Classic Hairy Cell Leukemia (HCL) is a rare, slow-growing blood cancer with an excellent long-term outlook. Most patients achieve complete remission and have a near-normal lifespan. Because it grows slowly, many patients do not need immediate treatment and begin with a 'watch and wait' approach.

Receiving a diagnosis of “leukemia” is life-altering and understandably frightening. However, it is important to know that Classic Hairy Cell Leukemia (HCL) is fundamentally different from the aggressive leukemias often portrayed in media. It is a highly treatable, slow-growing cancer of the blood and bone marrow [1][2].

Understanding Your Diagnosis

Classic Hairy Cell Leukemia is a rare type of B-cell cancer where the body makes too many B-lymphocytes (a type of white blood cell) [3]. These abnormal cells look “hairy” under a microscope because of tiny, thread-like projections on their surface [4].

This condition is considered indolent, meaning it is slow-growing [2]. Many patients do not require treatment the moment they are diagnosed; instead, doctors may use a “watch and wait” approach, also known as active surveillance, to monitor blood counts and symptoms over time [5].

Why This Disease is Unique

HCL is exceptionally rare, accounting for only about 2% of all adult leukemias [1]. Because of this rarity, many community oncologists—who treat more common cancers like breast or lung cancer—may only see one or two cases of HCL in their entire careers.

One of the most important features of classic HCL is the BRAF V600E mutation [4]. This is a specific genetic “typo” found in almost all cases of the classic form of the disease. Identifying this mutation is critical because:

  • It confirms you have the “classic” form rather than a different, sometimes more aggressive, “variant” form (HCL-v) [6][7].
  • It allows doctors to use targeted therapies if standard treatments are not suitable [8].

Outlook and Long-Term Health

The long-term outlook for classic HCL is excellent. Since the 1990s, the introduction of highly effective treatments has revolutionized how we manage this disease [9][10].

  • High Remission Rates: The vast majority of patients achieve a complete remission—meaning there is no visible evidence of the disease in the blood or bone marrow—following their first round of treatment [11][12].
  • Long-Term Survival: Most patients can expect a near-normal lifespan.
  • Chronic but Manageable: While HCL is currently considered a chronic condition that can return (relapse) years later, it remains very responsive to treatment even if it does come back [13].

Current clinical guidelines emphasize that HCL should be managed as a distinct disease, separate from other similar-looking blood cancers, to ensure patients receive the most effective, specialized care [14][7].

Explore the rest of this guide to learn more about Recognizing the Symptoms and Signs of HCL, The Genetic Engine of HCL: BRAF V600E, Making Sense of Your Labs and Pathology Report, Treatment Strategies for Classic HCL, Building Your Care Team and Preparing for Your First Visit, and Long-Term Monitoring and Survivorship.

In this guide

6 chapters

01

Recognizing the Symptoms and Signs of HCL

Learn the symptoms of Classic Hairy Cell Leukemia (HCL). Understand how low blood counts and an enlarged spleen cause fatigue, bruising, and frequent infections.

02

The Genetic Engine of HCL: BRAF V600E

Learn why the BRAF V600E mutation is the genetic engine of Classic Hairy Cell Leukemia (HCL), how it affects diagnosis, and what it means for your treatment.

03

Making Sense of Your Labs and Pathology Report

Learn how to read your Classic Hairy Cell Leukemia (HCL) pathology report. Understand your CBC lab results, BRAF V600E testing, and key diagnostic markers.

04

Treatment Strategies for Classic HCL

Learn about Classic Hairy Cell Leukemia (HCL) treatment strategies. Understand the watch and wait approach, frontline therapies, and options for relapsed HCL.

05

Building Your Care Team and Preparing for Your First Visit

Learn how to build your Classic Hairy Cell Leukemia (HCL) care team. Understand what medical records to bring to your first visit and how to vet specialists.

06

Long-Term Monitoring and Survivorship

Learn what to expect during Classic Hairy Cell Leukemia (HCL) survivorship. Understand your long-term monitoring schedule, signs of relapse, and health risks.

Common questions in this guide

What is Classic Hairy Cell Leukemia (HCL)?
Classic HCL is a rare, slow-growing blood cancer where your body makes too many abnormal white blood cells. These cells look 'hairy' under a microscope because they have tiny, thread-like projections on their surface.
Does an HCL diagnosis mean I need treatment right away?
Not necessarily. Because classic HCL is slow-growing, doctors often recommend active surveillance, also known as a 'watch and wait' approach. They will carefully monitor your blood counts and symptoms over time before deciding if and when to start active treatment.
What is the long-term outlook for someone with classic HCL?
The long-term outlook is excellent, with most patients achieving complete remission after their first treatment. While it is considered a chronic condition that can eventually return, it remains highly treatable and most patients experience a near-normal lifespan.
Why do doctors test for the BRAF V600E mutation in HCL?
The BRAF V600E mutation is a specific genetic change found in almost all classic HCL cases. Identifying it confirms you have the classic form of the disease rather than a more aggressive variant, and it helps guide whether targeted therapies are an option for you.
How is classic HCL different from other types of leukemia?
Unlike many aggressive leukemias, classic HCL is an indolent or slow-growing cancer. It accounts for only a tiny fraction of adult leukemias and is managed as a distinct, highly treatable chronic condition.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.How many patients with classic Hairy Cell Leukemia have you or this clinic treated in the past year?
  2. 2.What specific tests were used to confirm that I have 'classic' HCL rather than the 'variant' form?
  3. 3.Do I have the BRAF V600E mutation, and how does that affect my treatment options?
  4. 4.Based on my current blood counts and symptoms, do I need to start treatment immediately or can we 'watch and wait'?
  5. 5.If I need treatment, what is the likelihood that I will achieve a long-term complete remission?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (14)
  1. 1

    Hairy Cell Leukemia and Bone Pain.

    Streu E

    Oncology nursing forum 2016; (43(1)):18-21 doi:10.1188/16.ONF.18-21.

    PMID: 26679440
  2. 2

    Patients with relapsed/refractory hairy-cell leukemia.

    Paillassa J, Troussard X

    Cancer reports (Hoboken, N.J.) 2022; (5(3)):e1495 doi:10.1002/cnr2.1495.

    PMID: 34250762
  3. 3

    New Targeted Therapy Combination Holds Promise to Untangle Hairy Cell Leukemia.

    Soong D, Taylor J

    NEJM evidence 2023; (2(10)):EVIDe2300173 doi:10.1056/EVIDe2300173.

    PMID: 38320184
  4. 4

    Hairy cell leukaemia with unusual BRAF mutations.

    Maitre E, Macro M, Troussard X

    Journal of cellular and molecular medicine 2023; (27(17)):2626-2630 doi:10.1111/jcmm.17890.

    PMID: 37530550
  5. 5

    Hairy cell leukemia and COVID-19 adaptation of treatment guidelines.

    Grever M, Andritsos L, Banerji V, et al.

    Leukemia 2021; (35(7)):1864-1872 doi:10.1038/s41375-021-01257-7.

    PMID: 33947938
  6. 6

    Detection of activating MAP2K1 mutations in atypical hairy cell leukemia and hairy cell leukemia variant.

    Mason EF, Brown RD, Szeto DP, et al.

    Leukemia & lymphoma 2017; (58(1)):233-236 doi:10.1080/10428194.2016.1185786.

    PMID: 27241017
  7. 7

    Hairy cell leukemia 2022: Update on diagnosis, risk-stratification, and treatment.

    Troussard X, Maître E, Cornet E

    American journal of hematology 2022; (97(2)):226-236 doi:10.1002/ajh.26390.

    PMID: 34710243
  8. 8

    Clinical analysis of hairy cell leukemia: the rare indolent hematological malignancy.

    Huang H, Liu Y, Zeng M, et al.

    American journal of translational research 2024; (16(2)):466-476.

    PMID: 38463575
  9. 9

    Relative survival reaches a plateau in hairy cell leukemia: a population-based analysis in The Netherlands.

    Dinmohamed AG, Posthuma EFM, Visser O, et al.

    Blood 2018; (131(12)):1380-1383 doi:10.1182/blood-2017-12-820381.

    PMID: 29382643
  10. 10

    Analysis of a cohort of 279 patients with hairy-cell leukemia (HCL): 10 years of follow-up.

    Paillassa J, Cornet E, Noel S, et al.

    Blood cancer journal 2020; (10(5)):62 doi:10.1038/s41408-020-0328-z.

    PMID: 32461544
  11. 11

    A 3-decade multicenter European experience with cladribine as upfront treatment in 384 patients with hairy cell leukemia.

    Broccoli A, Argnani L, Cross M, et al.

    Blood advances 2022; (6(14)):4224-4227 doi:10.1182/bloodadvances.2022007854.

    PMID: 35584397
  12. 12

    Classic hairy cell leukemia with an aggressive presentation.

    Fugere T, Harley S, Godbole A

    Proceedings (Baylor University. Medical Center) 2021; (34(6)):721-723 doi:10.1080/08998280.2021.1934344.

    PMID: 34733001
  13. 13

    Treatment of hairy cell leukemia.

    Chihara D, Kreitman RJ

    Expert review of hematology 2020; (13(10)):1107-1117 doi:10.1080/17474086.2020.1819231.

    PMID: 32893700
  14. 14

    Recommendations for the Management of Patients with Hairy-Cell Leukemia and Hairy-Cell Leukemia-like Disorders: A Work by French-Speaking Experts and French Innovative Leukemia Organization (FILO) Group.

    Paillassa J, Maitre E, Belarbi Boudjerra N, et al.

    Cancers 2024; (16(12)) doi:10.3390/cancers16122185.

    PMID: 38927891

This page provides an educational overview of Classic Hairy Cell Leukemia. It does not replace professional medical advice, and you should always consult your hematology team regarding your specific diagnosis and treatment plan.

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