The short answer
Hairy cell leukemia usually grows slowly, so NCI lists watchful waiting when possible. Cladribine and pentostatin are the chemotherapy drugs commonly used, often with rituximab, and BRAF inhibitors and ibrutinib appear on the list too. Splenectomy is one option among several.
NCI lists watchful waiting when possible, meaning close monitoring with no drugs until signs or symptoms appear or change.
Cladribine and pentostatin are the anticancer drugs commonly used, and NCI lists both with or without rituximab.
NCI warns that these drugs may raise the risk of other cancers, especially Hodgkin and non-Hodgkin lymphoma, so long-term follow-up matters.
BRAF inhibitors, ibrutinib, bendamustine with rituximab, and splenectomy all appear on NCI's list of treatment options.
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The full explanation.
The short answer
Hairy cell leukemia is a rare blood cancer. Your bone marrow makes too many lymphocytes, a type of white blood cell. Under a microscope, these cells have tiny hair-like projections, which is how the disease got its name. It usually grows slowly, and some people do not need treatment right away. When treatment is needed, it often works very well.
Watchful waiting: a real option, not a delay
Say you have no symptoms, and your blood counts are not badly affected. Your team may recommend watchful waiting instead of treatment. This means close monitoring, with regular blood tests, but no drugs given yet. This is not a way of avoiding care. Starting treatment before it is needed adds side effects. It does not add benefit for many people with this diagnosis. Ask your team what specific changes in your blood counts or symptoms would prompt starting treatment.
Chemotherapy: the main treatment when you need it
Two chemotherapy drugs, cladribine and pentostatin, are the standard treatments for hairy cell leukemia. Both often produce long remissions. This means long periods with no sign of active disease. A newer drug, bendamustine, is being studied as another option. Ask your team which drug they recommend for you and why. The two standard options differ somewhat in how they are given and what side effects to expect.
Targeted therapy
Rituximab is a monoclonal antibody. This is a lab-made immune protein that targets a specific marker on cancer cells. It may be combined with chemotherapy or used on its own. BRAF inhibitors, including vemurafenib and dabrafenib, block a specific protein. A genetic change in hairy cell leukemia produces this protein. Trametinib works on a related pathway. Ibrutinib blocks a different protein, called Bruton's tyrosine kinase, that these cancer cells depend on. NCI lists BRAF inhibitors, rituximab and ibrutinib among the treatment options for this disease, and describes vemurafenib, dabrafenib, trametinib and ibrutinib as still being studied in it. Ask your team where each one sits in your own plan.
Surgery for an enlarged spleen
Hairy cell leukemia often enlarges the spleen. This is an organ where these cells tend to build up. If the spleen becomes large enough to cause problems, your team may recommend splenectomy, surgery to remove it. This is generally one option among several, not the automatic next step. Ask your team why they are or are not recommending it for you.
Side effects to expect
Chemotherapy drugs used for hairy cell leukemia commonly lower your blood counts for a period. This raises infection risk and can cause fatigue. NCI says cladribine and pentostatin may increase the risk of other types of cancer, especially Hodgkin lymphoma and non-Hodgkin lymphoma, and that long-term follow-up for second cancers is very important. Ask your team what monitoring they recommend afterward, and for how long. Side effects vary by which specific drug or combination you receive. Ask your team what to expect from your particular plan.
Which symptoms cannot wait
How you handle a fever of 100.4°F (38°C) or higher, the figure CDC uses, depends on whether you are having treatment. During or soon after cladribine or pentostatin, your infection-fighting blood cells are low, and CDC treats such a fever as a medical emergency. Call your care team immediately, day or night. If you cannot reach them quickly, go to an emergency department and tell them straight away that you are having chemotherapy. Without drug treatment, ring your team the same day for that temperature and follow their emergency instructions. Either way, call the same day for unusual bruising or bleeding, severe abdominal pain, which can point to a spleen problem, or any symptom your team has specifically told you to report right away.
What to ask your care team
- Do I need treatment now, or is watchful waiting appropriate for me?
- If I need treatment, would you recommend cladribine, pentostatin, or another option, and why?
- What side effects should I expect, and which need a same-day call?
- How will you monitor me for a second cancer or a return of hairy cell leukemia afterward?
Sources
Words to know
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Common questions
What is hairy cell leukemia?
It is a rare blood cancer in which your bone marrow makes too many lymphocytes, a type of white blood cell. Under a microscope these cells have tiny hair-like projections, which is how the disease got its name. It usually grows slowly, so some people do not need treatment right away, and when treatment is needed it often works very well.
Is watchful waiting just a way of delaying care?
No. If you have no symptoms and your blood counts are not badly affected, your team may recommend close monitoring with regular blood tests and no drugs yet. Starting treatment before it is needed adds side effects, and for many people with this diagnosis it does not add benefit. Ask what specific changes would prompt starting.
What is the standard treatment when it is needed?
Two chemotherapy drugs, cladribine and pentostatin, are the standard treatments, and both often produce long remissions. A newer drug, bendamustine, is being studied as another option. The two standard drugs differ somewhat in how they are given and in what side effects to expect, so ask which one your team recommends and why.
Where do targeted drugs fit in?
They are generally considered when standard chemotherapy has not worked well enough, or if the disease returns. Rituximab is a monoclonal antibody that may be combined with chemotherapy or used on its own. BRAF inhibitors, including vemurafenib and dabrafenib, block a protein produced by a genetic change in this disease. Trametinib works on a related pathway, and ibrutinib blocks Bruton's tyrosine kinase, a different protein these cells depend on.
Which symptoms cannot wait?
A fever of 100.5 degrees Fahrenheit — 38 °C is 100.4 °F; act at 100.4 °F — or higher, the figure CDC uses, is an emergency if you are on cladribine or pentostatin or finished a course in recent weeks. Call your care team immediately, day or night, and if you cannot reach them quickly go to an emergency department, because those drugs strip out the blood cells that fight infection. If you are on watchful waiting with no drug treatment, call your team the same day for that temperature and follow their emergency instructions. Call the same day as well for unusual bruising or bleeding, or severe abdominal pain, which can point to a spleen problem, or for any symptom your team has told you to report right away.
Questions to ask your doctor
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Sources last checked: 2026-08-13 what this meansLast updated: 2026-08-20Next planned review: 2027-01-22
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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