Hairy cell leukemia

Hairy cell leukemia (HCL) is an uncommon type of lymphocytic leukemia that starts in B cells, or B lymphocytes (a type of white blood cell). The B cells in HCL are different from those seen in chronic lymphocytic leukemia (CLL). Hairy cell leukemia is sometimes called classic or classical hairy cell leukemia.

HCL is called hairy cell leukemia because there are fine projections on the surface of the cancer cells that look like hair when they are viewed under a microscope.

About 2% of all lymphocytic leukemias in adults are HCL. It is much more common in men than in women. The average age at diagnosis is 50 years.

HCL is usually slow growing (chronic), but it often progresses (gets worse). Most people will eventually need treatment. It is highly treatable but rarely cured.

The most common symptoms of HCL are low blood cell counts and an enlarged spleen. The lymph nodes are usually not enlarged.

Many tests used to diagnose HCL are the same as the tests used to diagnose other forms of leukemia. A diagnosis of HCL is usually based on whether the cancer cells look hairy and if the cells have certain gene mutations. The BRAF-V600E mutation is unique to HCL and is rarely found in other B-cell chronic leukemias.

If HCL is diagnosed but the cells do not have the BRAF-V600E mutation, it is called variant HCL (vHCL). Most vHCL has a MAP2K1 gene mutation. Variant HCL is much less common than classic HCL, tends to be more aggressive and does not respond as well to standard HCL treatment.

Treatment is usually given if HCL starts to progress. Signs that the disease is progressing include symptoms getting worse, low blood cell counts and frequent infections.

Your healthcare team will create a treatment plan just for you. The plan is based on your health and specific information about the cancer. What you want is also important when planning treatment. HCL often progresses slowly, so you may not start treatment right away. You may be offered the following treatments for HCL.

Active observation means that your healthcare team watches the cancer closely for changes. They will use tests and exams to check if HCL is progressing or your condition is getting worse. You might not need other treatment right away if you don't have any symptoms or your blood cell counts are stable. Other treatment is given when you develop symptoms or there is disease progression.

This approach helps avoid side effects that can happen with treatments such as chemotherapy or targeted therapy. There is no evidence so far that people won't live as long when they get active observation compared to other treatments.

You may be offered active observation if:

• you don't have any symptoms of HCL
• the cancer is growing very slowly and isn't affecting your health

If you start having symptoms or they get worse, such as your blood cell counts staying low or your spleen getting larger and more uncomfortable, your healthcare team may decide to start other treatment. You may be offered the following treatment for first-line therapy for HCL.

Cladribine is the most common drug used to treat HCL. Cladribine is a type of chemotherapy. Chemotherapy uses drugs to destroy cancer cells. These drugs target rapidly dividing cells throughout the whole body. This means that chemotherapy kills cancer cells but it can also damage healthy cells. The drugs travel through the blood to reach and destroy cancer cells all over the body. This is called systemic therapy.

Rituximab (Rituxan, Ruxience, Riabni, Riximyo, Truxima) may also be added to cladribine. Rituximab is a type of targeted therapy. Targeted therapy uses drugs to target specific molecules (such as proteins) on cancer cells or inside them. These molecules help send signals that tell cells to grow or divide. By targeting these molecules, the drugs stop the growth and spread of cancer cells and limit harm to normal cells.

You may be offered the combination of cladribine and rituximab if you have variant HCL. This treatment increases the risk of infection, so the healthcare team may give you medicines to help prevent an infection.

Details on specific drugs change regularly. Find out more about sources of drug information and where to get details on specific drugs.

Relapsed, or recurrent, HCL means that the cancer has come back after it has been treated.

Refractory HCL means that the cancer did not respond to treatment.

You may be offered the following treatments for relapsed or refractory HCL:

• cladribine
• cladribine and rituximab

Vemurafenib (Zelboraf) is a type of targeted therapy called a BRAF inhibitor. It targets the BRAF-V600E gene. Vemurafenib may be offered for HCL that did not respond to cladribine treatment or relapsed after cladribine and rituximab combination treatment.

Ibrutinib (Imbruvica) is a type of targeted therapy called a Bruton's tyrosine kinase (BTK) inhibitor. Tyrosine kinases are a part of a protein that acts like a cell's on and off switch. They are enzymes that play an important role in a cell's growth and division. BTK inhibitors block these enzymes from sending signals that cause a cancer cell to grow. Ibrutinib may be offered for HCL that did not respond to first-line therapy.

Moxetumomab pasudotox (Lumoxiti) targets the CD22 gene on cancer cells. It has been shown to successfully treat refractory HCL, but it has serious side effects. Moxetumomab pasudotox is not currently approved for standard use in Canada. Your healthcare team may be able to get this drug through special drug access programs if there are no other treatment options left to try. You may have to pay for it yourself or find financial assistance to cover the cost.

Dabrafenib (Tafinlar), which is a BRAF inhibitor, may be combined with another drug called trametinib (Mekinist), which is a MEK inhibitor. These drugs are not currently approved for HCL in Canada, but they may be used in a clinical trial or under special situations.

Venetoclax (Venclexta) is a type of targeted therapy called a BCL2 inhibitor. Venetoclax is not currently approved to treat HCL in Canada, but may be used under special situations.

HCL and its treatments can cause certain problems, including infection, bleeding and low blood cell counts. If you develop these problems, you may be given:

• antibiotics to prevent and treat infections
• transfusions of red blood cells and platelets to raise low blood cell counts
• growth factors such as filgrastim (Neupogen and biosimilars) and pegfilgrastim (Neulasta and biosimilars)

Growth factors can help the body make white blood cells. They can shorten the length of time you have a low white blood cell count and so lower the risk of infection.

You may be asked if you want to join a clinical trial for HCL. Clinical trials look at new ways to prevent, find and treat cancer. Find out more about clinical trials.

Follow-up care lets your healthcare team keep track of your health for a period of time after treatment ends. This important part of cancer care is often shared among the cancer specialists and your family doctor. They will help you recover from treatment side effects and monitor you for any signs that the cancer has come back.

Follow-up care may not seem that important to you, especially if your treatment was long or very hard. You may find the idea of follow-up care stressful because it reminds you of your cancer experience or because you are worried about what a test might reveal. Talk to your healthcare team about how you feel and about why follow-up matters. Your healthcare team is there to help.

Don’t wait until your next scheduled appointment to report any new symptoms and symptoms that don’t go away.

Some of the tests done to diagnose HCL may be done again as follow-up to see how treatment is working. The results of these tests will let the healthcare team know if your condition has become worse or if the cancer has come back. If the cancer has come back, you and your healthcare team will discuss your treatment and care.