Hairy cell leukemia is a rare, slow-growing cancer of the blood in which your bone marrow makes too many B cells (lymphocytes), a type of white blood cell that fights infection. These abnormal cells look "hairy" under a microscope because of fine projections (villi) from their surface. As the number of leukemia cells increases, fewer healthy white blood cells, red blood cells and platelets are produced.

About 600 people are diagnosed with hairy cell leukemia each year in the United States. Hairy cell leukemia affects more men than women, and it occurs most commonly in middle-age or older adults. Children and teenagers don't get hairy cell leukemia.

Doctors aren't sure what causes hairy cell leukemia. Although there is no cure, new treatments offer an excellent chance of living cancer-free for at least 10 years. Doctors consider hairy cell leukemia a chronic form of cancer because treatments can lead to a remission for years, though hairy cell leukemia may never completely disappear.

Some people show no signs or symptoms of hairy cell leukemia, but a blood test for another disease or condition may inadvertently reveal hairy cell leukemia in their blood.

Other times people with hairy cell leukemia experience signs and symptoms common to a number of diseases and conditions, such as:

• A feeling of fullness in your abdomen that may make it uncomfortable to eat more than a little at a time
• Fatigue
• Easy bruising
• Recurring infections
• Weakness
• Weight loss

Cancers are caused by a defect in your DNA. In the case of hairy cell leukemia, mutations in the DNA cause your bone marrow stem cells to create too many white blood cells that don't work properly. It isn't clear what causes the DNA mutations that lead to hairy cell leukemia.

Certain factors may increase your risk of developing hairy cell leukemia. Not all research studies agree on what factors increase your risk of the disease. Some research indicates that your risk of hairy cell leukemia increases based on your:

• Family history of blood cancers. Hairy cell leukemia is sometimes found in families with a history of this and other blood cancers.
• Ashkenazi Jewish heritage. Ashkenazi Jewish men may have a higher risk of hairy cell leukemia.
• Personal history of cancer. If you've had another type of cancer, you're more likely to develop hairy cell leukemia.
• Exposure to radiation. People who work around X-ray machines and other medical equipment that gives off ionizing radiation may have a higher risk of developing hairy cell leukemia, though some studies haven't found this to be the case.
• Exposure to chemicals. Chemicals, such as those used in agricultural and petroleum products, could play a role in hairy cell leukemia development. Some studies have found this not to be the case.
• Exposure to sawdust. Results have been mixed, but some studies have found a link between working with wood and sawdust and an increased risk of hairy cell leukemia.

Hairy cell leukemia doesn't always cause signs and symptoms that would prompt you to see your doctor. If you experience signs and symptoms that concern you, make an appointment with your doctor. Otherwise, stick to your regular appointment schedule. Ask your doctor how often you should have routine exams.

If your doctor suspects you have hairy cell leukemia, he or she will look for three indicators:

• Enlarged spleen
• Reduced number of all blood cell types
• Hairy cell leukemia cells in your blood

To accomplish this, your doctor may use a number of tests and exams, such as:

Physical exam
By feeling your spleen — an oval-shaped organ on the left side of your upper abdomen — your doctor can determine if it's enlarged. An enlarged spleen may cause a sensation of fullness in your abdomen that makes it uncomfortable to eat. Your doctor may also check for enlarged lymph nodes that may indicate cancer.

Blood tests
Your doctor uses blood tests, such as the complete blood count (CBC), to monitor the levels of blood cells in your blood. People with hairy cell leukemia have low levels of all three types of blood cells — red blood cells, white blood cells and platelets. Another blood test called a peripheral blood smear looks for hairy cell leukemia cells in a sample of your blood.

Bone marrow biopsy
During a bone marrow biopsy, a health care professional removes a small amount of bone marrow from your hip area. This sample is used to look for hairy cell leukemia cells and to monitor your healthy blood cells.

Computerized tomography (CT) scan
A CT scan shows detailed images of the inside of your body. Your doctor may order a CT scan to detect enlargement of your spleen and your lymph nodes.

Your doctor will want to rule out other diseases that are similar to hairy cell leukemia. Variant hairy cell leukemia, for instance, has many of the same features as hairy cell leukemia, but the variant form causes a high white blood cell count, rather than a very low count. Other diseases mistaken for hairy cell leukemia include: prolymphatic leukemia, chronic lymphocytic leukemia and splenic marginal zone leukemia.

Hairy cell leukemia progresses very slowly and sometimes remains stable for many years. For this reason, few complications of the disease exist. However, untreated hairy cell leukemia that progresses can lead to serious complications, such as:

• Infections. Low white blood cell counts put you at risk of infections that your body might otherwise fight off.
• Bleeding. Low platelet counts make it hard for your body to stop bleeding once it starts. If you have a mildly low platelet count you might notice that you bruise more easily. Very low platelet counts can cause spontaneous bleeding from the nose or gums.
• Anemia. A low red blood cell count means fewer cells are available to carry oxygen throughout your body. This is called anemia. Anemia causes fatigue.
• Ruptured spleen. Splenic rupture is a life-threatening condition that requires emergency surgery to remove your spleen. Hairy cell leukemia cells fill the spleen, causing it to enlarge. Eventually the extra cells cause the spleen to burst, though this complication is very rare.

Treatment isn't always necessary for people with hairy cell leukemia. Because this cancer progresses very slowly and sometimes doesn't progress at all, some people prefer to wait to treat their cancer only if it causes signs and symptoms. The majority of people with hairy cell leukemia will eventually need treatment.

Though you may be eager to rid your body of cancer if you've been diagnosed with hairy cell leukemia, know that there's no advantage to early treatment. Unlike some other types of cancer, hairy cell leukemia is quite treatable at all stages, meaning that waiting to treat your cancer won't make remission any less likely.

If your hairy cell leukemia causes signs and symptoms, you may decide to undergo treatment. There is no cure for hairy cell leukemia. But the good news is that new treatments are effective at putting hairy cell leukemia in remission for years.

Chemotherapy
Doctors consider chemotherapy drugs the first line of treatment for hairy cell leukemia. About 90 percent of people will experience complete or partial remission through the use of chemotherapy. Two chemotherapy drugs are used in hairy cell leukemia:

• Cladribine (Leustatin). Most treatment regimens for hairy cell leukemia begin with cladribine. You receive a continuous infusion of the drug into a vein over seven days. Most people who receive cladribine experience a complete remission that can last for several years. If your hairy cell leukemia returns, you can be treated with cladribine again. Side effects of cladribine include infection and fever.
• Pentostatin (Nipent). Pentostatin causes remission rates similar to cladribine, but it's given on a different schedule. People who take pentostatin receive infusions every other week for three to six months. Side effects of pentostatin include fever, infection, sensitivity to light, eye inflammation (keratoconjunctivitis), and nausea and vomiting.

About 10 percent of people with hairy cell leukemia are resistant to chemotherapy, meaning they won't achieve remission using these drugs. Other people can't take chemotherapy. For instance, people with infections must avoid chemotherapy because these powerful drugs suppress the immune system and can make small infections much worse.

Biological treatments
Biological therapy (immunotherapy) attempts to make cancer cells more recognizable to your immune system. Once your immune system identifies cancer cells as intruders, it can set about destroying your cancer. Two types of biological treatments are used in hairy cell leukemia:

• Interferon alpha. Interferon alpha was the first biologic drug approved for cancer treatment. You might use interferon alpha if chemotherapy hasn't been effective or if you can't take chemotherapy. Most people experience partial remission with interferon alpha, which is taken over a year. Side effects include flu-like symptoms, such as fever and fatigue.
• Rituximab (Rituxan). Rituximab is a monoclonal antibody approved to treat non-Hodgkin's lymphoma, though it's sometimes used in hairy cell leukemia. If chemotherapy drugs haven't worked for you or you can't take chemotherapy, your doctor might consider rituximab. Side effects of rituximab include bleeding, fatigue, headache and infection.

Surgery
Surgery to remove your spleen (splenectomy) was the first treatment used in hairy cell leukemia, though it's used only rarely today. Your doctor might recommend splenectomy if your spleen ruptures or if it's enlarged and causing you pain. Though removing your spleen can't cure hairy cell leukemia, it can usually restore normal blood counts. For that reason, splenectomy may be useful in people with uncontrollable infections. All surgery carries a risk of bleeding and infection. Removal of your spleen can cause inflammation of your blood vessels (vasculitis) and can make you susceptible to infection.

Doctors consider hairy cell leukemia a chronic form of cancer because it never completely goes away. Even if you achieve remission with your treatment, you'll likely require follow-up visits with your doctor to monitor your cancer and your blood counts. Knowing that your cancer could come back at any time can be stressful. To help you cope, you might consider trying to:

• Find out all you can about hairy cell leukemia. Learn as much as you can about your cancer and its treatment. Having a better idea of what to expect from treatment and life after treatment can make you feel more in control of your cancer. Ask your doctor, nurse or other health care professional to recommend some reliable sources of information to get you started.
• Connect with other cancer survivors. While friends and family provide an important support network during your cancer experience, they can't always understand what it's like to face cancer. Other cancer survivors provide a unique network of support. Ask your doctor or other member of your health care team about support groups or organizations in your community that can connect you with other cancer survivors. Organizations such as the American Cancer Society and the Leukemia and Lymphoma Society offer online chat rooms and discussion boards.
• Take care of yourself. You can't control whether your hairy cell leukemia comes back, but you can control other aspects of your health. Take care of your body by eating a balanced diet with plenty of fruits and vegetables and by exercising regularly. A healthy body can more easily fend off infections and, should you ever need to be treated for cancer again, you'll be better able to cope with the side effects of treatment.