Hairy Cell Leukaemia
Hairy cell leukaemia is a rare type of cancer that grows slowly in the blood and bone marrow, named after the unusual “hairy” appearance of the affected cells when viewed under a microscope.
Table of contents
- What is hairy cell leukaemia?
- Parts of the body affected
- Causes and risk factors
- Signs and symptoms
- Diagnosing hairy cell leukaemia
- Treatment approaches
- Outlook and life expectancy
- Hairy cell leukaemia variant
What is hairy cell leukaemia?
Hairy cell leukaemia is a rare form of cancer affecting the blood and bone marrow. It develops when the body makes too many abnormal B-cells, which are a type of white blood cell that normally helps fight off infections[1]. In this condition, these cells develop changes that turn them into cancer cells. The disease gets its name from the way these cells look under a microscope—they have tiny, hair-like projections sticking out from their surface[1].
This type of leukaemia develops slowly and may not cause symptoms for many years[1]. It is considered a chronic condition, meaning it persists over time but can often be controlled with treatment. Hairy cell leukaemia accounts for only about 2% of all leukaemias, with approximately 1,000 new cases diagnosed each year in the United States[2][6].
The abnormal hairy cells keep living when healthy cells would naturally die as part of the body’s normal cell life cycle[1]. As these cells build up in the bone marrow, they leave less room for healthy blood cells to develop. This can lead to low levels of red blood cells, normal white blood cells, and platelets (cells that help blood clot)[3].
Parts of the body affected
- Bone marrow
- Blood
- Spleen
- Liver
- Lymph nodes
Hairy cell leukaemia primarily affects the bone marrow, which is the soft, spongy tissue inside bones where blood cells are made[3]. The abnormal cells build up in the bone marrow and then spill over into the bloodstream. From there, they can spread to other parts of the body.
The spleen is very commonly affected in this condition. In fact, more than 90% of patients have an enlarged spleen at the time of diagnosis[2]. The spleen is located in the upper left side of the abdomen. When it becomes enlarged, it can cause a feeling of fullness or discomfort in that area[4].
The liver may also become affected, causing it to swell. This can lead to pain in the lower right side of the abdomen[4]. Lymph nodes, which are small glands that are part of the immune system, can also accumulate hairy cells, though swollen lymph nodes on physical examination are less common[2].
Causes and risk factors
The exact cause of hairy cell leukaemia is not known[1]. However, researchers have discovered that about 90% to 95% of people with this disease have a specific change in a gene called BRAF V600E[4][6]. This gene normally helps control cell growth. When it changes, cells can divide and survive without proper control, eventually becoming cancerous. This genetic change happens during a person’s lifetime—it is not inherited from parents[9].
Several factors may increase the risk of developing hairy cell leukaemia. The condition most commonly affects middle-aged adults, with the average age at diagnosis being around 55 to 58 years[4][6]. Men are affected much more often than women, with a ratio of about 4 to 1[6].
Exposure to certain chemicals may play a role. Studies have suggested a possible link with exposure to Agent Orange, a herbicide used during the Vietnam War[4][8]. Some research has also found a correlation with farming and gardening, though this does not necessarily mean these activities cause the disease[8]. Exposure to pesticides and working with large animals have also been identified as possible risk factors[9].
Signs and symptoms
Many people with hairy cell leukaemia do not have symptoms when first diagnosed. Sometimes a doctor discovers the condition by accident during routine blood tests for another reason[1][5]. Because the disease develops gradually, symptoms may appear slowly over time.
When symptoms do occur, they are often related to low blood cell counts. Fatigue and weakness are common because of low levels of red blood cells, a condition called anaemia[3][4]. People may also experience shortness of breath during everyday activities.
Frequent infections and fevers can develop when white blood cell levels drop too low[3][4]. The body becomes less able to fight off germs and infections. Easy bruising and bleeding, such as nosebleeds or bleeding gums, may occur when platelet counts are low[3][4].
An enlarged spleen can cause pain or a feeling of fullness below the ribs on the left side[3][4]. This fullness may make it uncomfortable to eat more than a small amount at a time. Some people experience unexplained weight loss. If the liver is enlarged, there may be pain in the lower right side of the abdomen[4].
Less commonly, people may notice painless lumps in the neck, underarms, stomach, or groin area, which are swollen lymph nodes[3].
Diagnosing hairy cell leukaemia
Diagnosis begins with a physical examination and discussion of medical history[4]. The doctor may feel the abdomen to check if the spleen or liver is enlarged. Several tests are used to confirm the diagnosis.
A complete blood count (CBC) measures the levels of different types of blood cells. In hairy cell leukaemia, this test often shows low levels of red blood cells, white blood cells, and platelets[3][4]. Another important finding is a reduction or complete absence of a specific type of white blood cell called monocytes[2].
A peripheral blood smear involves placing a blood sample on a slide and examining it under a microscope. This test may reveal the characteristic hairy cells with their unusual projections[2][4]. However, hairy cells are not always visible in the blood, as they may only be present in the bone marrow.
A bone marrow biopsy is the most reliable test for diagnosis. A doctor uses a thin needle to remove a small sample of bone marrow, usually from the hip area[4]. This sample is examined for the presence of hairy cells. The bone marrow in hairy cell leukaemia is often difficult to aspirate because it becomes fibrotic, meaning it contains more fibrous tissue than normal[6].
Immunophenotyping is a test that identifies cells based on special markers on their surface. Hairy cells have a characteristic pattern of markers, including CD19, CD20, CD11c, CD25, CD103, and CD123[2]. Testing for the BRAF V600E gene mutation can also help confirm the diagnosis[6].
Imaging tests such as CT scans or ultrasound may be used to check the size of the spleen, liver, and lymph nodes[4].
Treatment approaches
Not everyone with hairy cell leukaemia needs immediate treatment. Because the disease often progresses slowly, some people can be monitored without starting treatment right away[4]. This approach is called active surveillance or watchful waiting. During this time, patients see their doctor every three to six months for check-ups and blood tests.
When treatment becomes necessary, chemotherapy is the main approach. The most commonly used chemotherapy drugs for hairy cell leukaemia are cladribine and pentostatin[12].
Cladribine is usually given as an injection just under the skin every day for 5 days in a row[12]. Some people receive it as a continuous drip into a vein for 7 days. Most people need only one course of cladribine treatment. This drug is very effective, with 85% to 90% of people achieving complete remission, meaning all signs of cancer disappear[9].
Pentostatin is given as an infusion into a vein every 2 weeks[12]. Treatment continues until the leukaemia is under control or has disappeared, which usually takes between 3 to 6 months.
If the disease comes back after initial treatment (called a relapse) or if the first treatment does not work well enough, other options are available. These may include repeating chemotherapy, sometimes combined with a targeted drug called rituximab. Rituximab is a type of medicine that targets specific markers on cancer cells[12].
Other treatments that may be used include drugs that target the BRAF gene mutation, such as vemurafenib or dabrafenib[17]. Another drug called ibrutinib may also be an option[17].
In rare cases, surgical removal of the spleen may be considered, particularly if the spleen is very enlarged and causing symptoms[13].
Outlook and life expectancy
Hairy cell leukaemia is considered treatable, though not curable[2]. The outlook for most people with this condition is very good. With treatment, many people can expect to have a normal life expectancy[5][9].
The disease can be kept under control for many years with treatment[5]. Around 50% of people who achieve remission remain free of the disease for 10 years or longer[9]. However, the disease can come back (relapse) in some people, requiring additional treatment.
After successful treatment, regular follow-up care is important. People need ongoing monitoring to check for any signs that the disease may be returning. This typically involves periodic blood tests and physical examinations.
Some complications can occur. The disease and its treatment can make it harder for the body to fight infections[4]. There is also a slightly increased risk of developing a second, different type of cancer years after treatment[4].
Hairy cell leukaemia variant
There is a separate condition called hairy cell leukaemia variant (HCL-V)[5]. Although it has a similar name and the cells look somewhat alike under a microscope, it is considered a different disease from classic hairy cell leukaemia. Hairy cell leukaemia variant accounts for about 10% of hairy cell cases[6].
The variant form is more aggressive and progresses faster than classic hairy cell leukaemia[1][6]. People with the variant typically have higher white blood cell counts. The cancer cells in the variant form lack certain markers found in classic hairy cell leukaemia, such as CD25 and CD123[2][6]. They also do not have the BRAF gene mutation seen in most classic cases.
The variant form does not respond as well to the standard chemotherapy treatments used for classic hairy cell leukaemia[6]. People with hairy cell leukaemia variant tend to have shorter periods of remission and more aggressive disease courses.
