Hairy Cell Leukemia: What It Is, the 6 Warning Signs, and How Treatment Keeps It Under Control
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Source currency note: This guide reflects clinical content reviewed and dated March 8, 2024. Medical guidance changes over time; always confirm current recommendations with a licensed healthcare professional.
TL;DR
Hairy cell leukemia is a slow-growing cancer of B cells, a type of white blood cell that fights germs. It is named for the thin hair-like projections leukemia cells show under a microscope. The disease often causes no symptoms and is sometimes found by accident during a blood test for another condition. When symptoms do appear, they include belly fullness, fatigue, easy bruising, recurring infections, weakness, and unexplained weight loss. It most often strikes people in their 50s or 60s and is more common in men. Treatment — usually chemotherapy, sometimes targeted drug therapy — controls the disease very effectively and often produces remission, though it does not cure it completely. Many people live with this disease for many years with a normal daily life.
Quick Answer
Hairy cell leukemia is a slow-growing cancer of B cells (B lymphocytes), a type of white blood cell. The cancer cells look "hairy" under a microscope because thin projections stick out from them.
The cancer develops when B cells acquire DNA changes that make the body produce too many non-working B cells, which crowd out healthy blood cells in the bone marrow and other organs.
It often causes no symptoms and may be discovered by accident during a routine blood test; when symptoms appear, they include belly fullness, fatigue, easy bruising, recurring infections, weakness, and unexplained weight loss.
Most people diagnosed are in their 50s or 60s, the disease is more common in men, and it is rare in children.
Diagnosis involves a physical exam of the spleen, a complete blood count (CBC), a peripheral blood smear, a bone marrow biopsy, and a CT scan.
Treatment — usually chemotherapy given by shot or IV, sometimes targeted drug therapy — often achieves complete or partial remission, meaning no signs of cancer; treatment may not be needed right away because the disease grows very slowly.
Treatments control the disease but do not make it go away completely; with care, most people can live with hairy cell leukemia for many years and continue normal daily life.
What Is Hairy Cell Leukemia?
Hairy cell leukemia is a cancer of the white blood cells — the cells that help the body fight off germs. There are several types of white blood cells, and the type involved in hairy cell leukemia is the B cell (also called a B lymphocyte).
In this disease, the body makes too many B cells. These cells do not look like healthy B cells. Instead, they have undergone changes and become leukemia cells. Those leukemia cells look "hairy" under a microscope — the "hair" is actually thin projections that stick out from the cell surface.
The leukemia cells keep living when healthy cells would die as part of the natural cell life cycle. As a result, the leukemia cells build up in the body and cause symptoms.
Hairy cell leukemia often gets worse slowly. Because of this, treatment might not need to start right away. When treatment is needed, it is usually chemotherapy, and it is very effective at controlling the disease.
Scientists have also found a type of cancer that looks like hairy cell leukemia but gets worse much faster. That other cancer is called hairy cell leukemia variant. Even though the names are similar, the variant is considered a separate type of cancer.
Hairy Cell Leukemia: Key Facts at a Glance
Question | Answer |
What is it? | A slow-growing cancer of B cells, a type of white blood cell |
Why "hairy"? | The leukemia cells have thin hair-like projections visible under a microscope |
How fast does it grow? | Very slowly; sometimes it stays stable for many years |
Who gets it most? | Adults in their 50s or 60s; more common in men; rare in children |
Does it always cause symptoms? | No — it is sometimes found by accident during a blood test for another condition |
Can it be cured? | Treatments control it very effectively but do not make it go away completely |
What is remission? | Having no signs of cancer, which many people reach after chemotherapy |
Symptoms: The 6 Signs to Watch For
Hairy cell leukemia might not cause symptoms at all. Sometimes a healthcare provider finds it by accident during a blood test done for another condition.
When it does cause symptoms, hairy cell leukemia might cause the following:
Symptom | What You Would Notice |
Belly fullness | A feeling of fullness in your belly that may make it uncomfortable to eat more than a little at a time |
Fatigue | Feeling very tired, often from anemia (too few red blood cells) |
Easy bruising | Bruising easily; possible bleeding from the nose or gums |
Recurring infections | Getting infections more often because the body cannot make enough healthy white blood cells |
Weakness | A general lack of strength and energy |
Unexplained weight loss | Losing weight without trying |
When to See a Doctor
Make an appointment with your healthcare provider if you have any persistent signs and symptoms that worry you. Early blood tests are what often catch hairy cell leukemia before symptoms become serious.
Causes: What Happens in the Body
It is not clear what causes hairy cell leukemia. What is known is how the disease develops.
Hairy cell leukemia begins in the white blood cells. It happens when B cells develop changes in their DNA. A cell's DNA contains the instructions that tell a cell what to do. In this disease, the DNA changes tell the B cells to make a lot more B cells that do not work right. These cells go on living when healthy cells would die as part of the natural cell life cycle.
The B cells that do not work right crowd out healthy blood cells in the bone marrow and other organs. This crowding is what leads to the symptoms and complications of hairy cell leukemia. For example, the extra cells can cause swelling in the spleen, liver, and lymph nodes. If there is not enough room for healthy blood cells, this can lead to frequent infections, easy bruising, and feeling very tired.
Risk Factors
Risk Factor | What It Means |
Older adults | Hairy cell leukemia can happen at any age, but most people diagnosed are in their 50s or 60s |
Being male | It can happen to anyone, but it is more likely in males |
Childhood rarity | Hairy cell leukemia is rare in children |
Complications: What Can Go Wrong
Hairy cell leukemia often gets worse very slowly. Sometimes it stays stable for many years. For this reason, few complications of the disease occur.
Too Few Healthy Blood Cells
If there are too many leukemia cells in the body, they can crowd out the healthy blood cells. That can lead to three main problems:
Complication | Why It Happens | What You Experience |
Infections | Your body needs healthy white blood cells to fight off germs; without enough of them, you get more infections | Frequent or recurring infections |
Bleeding | Your body needs healthy platelet cells to control bleeding; low platelets mean less protection | Easier bruising; bleeding from the nose or gums |
Anemia | Anemia means having too few red blood cells, which carry oxygen through your body | Feeling very tired |
Increased Risk of Other Cancers
Some studies found that people with hairy cell leukemia have an increased risk of other types of cancer. These include non-Hodgkin's lymphoma, Hodgkin's lymphoma, and others. It is not clear whether the other cancers are caused by hairy cell leukemia itself or by cancer treatments.
How Hairy Cell Leukemia Is Diagnosed
To diagnose hairy cell leukemia, your healthcare provider may recommend a series of tests. The spleen — an oval-shaped organ about the size of your fist, located on the left side of the upper abdomen — plays a central role, because swelling in it is one of the clearest clues.
Test | What Happens | What It Shows |
Physical exam | Your provider feels your spleen to see if it is too big | An enlarged spleen can cause belly fullness and pain or discomfort when eating |
Complete blood count (CBC) with differential | A blood test measuring the levels of blood cells in your blood | All three cell types — red blood cells, white blood cells, and platelets — may be too low |
Peripheral blood smear | A lab looks at your blood under the microscope | The hairy cell leukemia cells themselves |
Bone marrow biopsy | A small amount of bone marrow is removed from your hip area for testing; a thin needle removes liquid marrow, and a biopsy often done at the same time also removes a small piece of bone tissue | Hairy cell leukemia cells in the marrow |
Lab tests on the leukemia cells | Cells collected from blood and bone marrow are tested in a lab, including DNA changes | Helps your provider understand your prognosis and the best treatments for you |
CT scan | A computerized tomography scan produces detailed images of the inside of your body | Swelling in the spleen and lymph nodes |
Treatment: Watch-and-Wait, Chemotherapy, and Targeted Therapy
Hairy cell leukemia treatments are good at controlling the disease. They cannot make it go away completely. Instead, treatments can control the cancer so that you can go about your life as usual. People with hairy cell leukemia can live with the disease for many years.
Treatment Might Not Need to Start Right Away
Treatment for hairy cell leukemia does not always need to start right away. This cancer often gets worse very slowly over time. You might choose to wait and have treatment if the cancer starts to cause symptoms.
If you do not have treatment right away, you will have regular appointments with your healthcare provider. You might have blood tests to see if the hairy cell leukemia is getting worse. Most people with hairy cell leukemia will eventually need treatment.
Chemotherapy
Chemotherapy is a drug treatment that uses powerful drugs to kill cancer cells. It is often the first treatment for hairy cell leukemia, and it is very effective for this disease. Most people get a complete or partial remission after chemotherapy — remission means you have no signs of cancer.
Chemotherapy for hairy cell leukemia can be given as a shot, or it can be given as an infusion into a vein.
If your hairy cell leukemia comes back, your provider might recommend repeating chemotherapy with the same drug or trying a different drug. Another option may be targeted drug therapy.
Targeted Drug Therapy
Targeted drug therapy attacks specific chemicals present within cancer cells. By blocking these chemicals, targeted drug treatments can cause cancer cells to die.
Targeted drug therapy is sometimes used as a first treatment for hairy cell leukemia, and it can be used together with chemotherapy. More often, targeted therapy is an option if the cancer comes back after chemotherapy. Your healthcare provider will have your cancer cells tested to see whether targeted drug therapy is likely to work for you.
Clinical Trials
Clinical trials test new treatments, interventions, and tests as a means to prevent, detect, treat, or manage hairy cell leukemia. Ask your healthcare team whether a trial may be right for you.
Treatment Comparison: Chemotherapy vs. Targeted Drug Therapy
Factor | Chemotherapy | Targeted Drug Therapy |
How it works | Powerful drugs kill cancer cells | Attacks specific chemicals inside cancer cells; blocking them causes the cells to die |
When it is used | Often the first treatment | Sometimes first; more often if cancer returns after chemotherapy |
How it is given | As a shot, or as an infusion into a vein | Given under provider guidance after cell testing |
How effective | Very effective; most people reach complete or partial remission | An option when cells are tested as likely to respond |
Used together? | Can be combined with targeted therapy | Can be used with chemotherapy |
Alternative Medicine: What Actually Helps
No alternative medicines are helpful for treating hairy cell leukemia. However, alternative approaches might be helpful in other ways — helping you cope with the stress of a cancer diagnosis and the side effects of treatment.
Talk to your healthcare provider about options such as art therapy, exercise, meditation, music therapy, relaxation exercises, and spirituality.
Coping and Support
A cancer diagnosis can feel overwhelming. Three approaches can help.
First, find out enough to feel comfortable making decisions about your care. Learning about hairy cell leukemia and its treatments can help you feel more confident about choosing your treatment path. Ask your healthcare provider to suggest reliable sources of information to get you started.
Second, connect with other cancer survivors. Friends and family provide an important support network during your cancer experience, but they cannot always understand what it is like to face cancer. Other cancer survivors provide a unique network of support. Ask your provider about support groups or organizations in your community. Organizations such as the Hairy Cell Leukemia Foundation and the Leukemia & Lymphoma Society offer ways to connect with others online.
Third, take care of yourself. You cannot control whether your hairy cell leukemia comes back, but you can control other aspects of your health. Eat a balanced diet with plenty of fruits and vegetables, exercise regularly, get enough sleep so that you wake up feeling refreshed, and find healthy ways to cope with life's stresses.
Preparing for Your Appointment
Start by seeing your usual healthcare provider if you have any symptoms that worry you. If your provider suspects you may have hairy cell leukemia, they may suggest that you see a specialist. This might be a doctor who treats diseases of the blood and bone marrow — a doctor called a hematologist.
Appointments can be brief, so it is a good idea to be prepared: be aware of any pre-appointment restrictions (ask when making the appointment); write down any symptoms you are experiencing, including any that may seem unrelated; write down key personal information, including major stresses or recent life changes; make a list of all medications, vitamins, or supplements you are taking; consider taking a family member or friend along; and write down questions to ask your doctor, ordered from most important to least important.
Useful questions to ask your doctor include: What kinds of tests do I need? Will I need treatment for my hairy cell leukemia? If I don't have treatment, will my leukemia worsen? If I need treatment, what are my options? Will treatment cure my hairy cell leukemia? What are the side effects of each treatment option? How will cancer treatment affect my daily life? Should I see a specialist, and will my insurance cover it?
Expect your doctor to ask when you began having symptoms, whether your symptoms have been continuous or occasional, how severe your symptoms are, what, if anything, seems to improve your symptoms, and what, if anything, makes your symptoms worse.
Conclusion: What to Do Next
Hairy cell leukemia sounds frightening, but it is among the most manageable blood cancers. It grows very slowly, it is sometimes found by accident before symptoms ever appear, and its treatments — especially chemotherapy — are very effective at bringing remission. Most people go on living with the disease for many years while continuing their normal daily lives.
If you have noticed persistent belly fullness, fatigue, easy bruising, recurring infections, weakness, or unexplained weight loss, the most important step is simple: book an appointment with your healthcare provider this week. A blood test is often all it takes to start the conversation, and early questions give you more options. If cancer is confirmed, ask for a referral to a hematologist and take a trusted friend or family member along to your appointment.
Frequently Asked Questions
Can hairy cell leukemia be cured?
Treatments are very good at controlling hairy cell leukemia and often produce remission — no signs of cancer — but they cannot make the disease go away completely. Most people live with the condition for many years and go about their normal daily lives.
Is hairy cell leukemia contagious or caused by lifestyle?
It is not clear what causes hairy cell leukemia. It develops when B cells acquire DNA changes that make the body produce too many non-working cells. Nothing suggests it is contagious or caused by anything a person did.
Who is most at risk for hairy cell leukemia?
Most people diagnosed are in their 50s or 60s, the disease is more common in men, and it is rare in children. It can, however, happen at any age.
How is hairy cell leukemia diagnosed?
Diagnosis typically involves a physical exam of the spleen, a complete blood count (CBC) with differential, a peripheral blood smear (blood viewed under a microscope), a bone marrow biopsy from the hip area, lab tests on the leukemia cells' DNA, and a CT scan to look for swelling in the spleen and lymph nodes.
Do I need treatment right away?
Not necessarily. Because the disease grows very slowly, treatment might not need to start right away. If you wait, you will have regular appointments and blood tests to monitor whether the cancer is worsening. Most people with hairy cell leukemia will eventually need treatment.
What is the difference between hairy cell leukemia and the variant?
Hairy cell leukemia variant looks like hairy cell leukemia but gets worse much faster. It is considered a separate type of cancer, even though the names are similar.
References
Health information, not medical advice. This article is for general education and is not a substitute for professional diagnosis or treatment. Always consult a qualified healthcare provider about your own health, and seek emergency care for urgent symptoms.
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