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About Hairy Cell Leukemia

Hairy cell leukemia is a rare type of leukemia, or cancer of the immune cells. In HCL, the bone marrow makes too many lymphocytes (a type of white blood cell). The disease is called hairy cell leukemia because the leukemia cells look “hairy” when viewed under a microscope. It tends to be a slow-growing type of leukemia and is generally treated with chemotherapy.

This disease is characterized by the production of atypical B-lymphocytes, which are immune cells that are produced in the bone marrow (spongy material inside bones). B-lymphocytes have a specific function in aiding the body to fight infection. When hairy cell leukemia develops, the cancerous lymphocytes accumulate in the blood, bone marrow, lymph nodes and spleen. This results in overcrowding of these areas, suppressing the formation and function of blood cells and immune cells that are normally present, particularly in the bone marrow. Additionally, the cancerous lymphocytes themselves do not function normally, which leads to a further decrease in the ability of the body to fight infection. Standard treatment for hairy cell leukemia consists of chemotherapy, biological therapy (utilizing the body’s immune system to fight cancer) and/or high-dose chemotherapy with stem cell transplantation.

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Diagnostic Tests for Hairy Cell Leukemia

Diagnosis of HCL is made by routine bone marrow examination. According to an article published in The Lancet, a marker identified by gene profiling referred to as Annexin A1 (ANXA1) can help distinguish hairy cell leukemia from other different kinds of leukemia because it is expressed in 97% of hairy cell leukemias.

Treatment of Hairy Cell Leukemia

  • Cladrabine 2-chlorodeoxyadenosine
  • Pentostatin
  • Zelboraf (vemurafenib)


Hairy cell leukemia patients who are treated with the chemotherapy drug pentostatin may achieve long-term survival. Although pentostatin has been shown to exert anti-cancer properties in the treatment of hairy cell leukemia, there is little data regarding long-term outcomes of patients with this disease. Since hairy cell leukemia is a rare cancer, overall data collection has been relatively sparse. Because few long-term statistics have been available, establishing superior treatment methods for optimal long term outcomes for patients with this disease has been difficult.

Researchers from several U.S. and Canadian medical centers have jointly evaluated long-term outcomes of almost 250 patients with hairy cell leukemia who were treated with pentostatin. Approximately 9 years following treatment, only 2 deaths in the entire group of patients were attributed to leukemia. Additionally, 173 patients achieved a complete disappearance of cancer following treatment with pentostatin, with 85% of these patients remaining cancer free 5 years following treatment.

These results indicate that pentostatin appears to be highly effective in the treatment of hairy cell leukemia, offering patients with this disease hope for possible long-term survival. These results are important in providing long-term outcome data regarding treatment of hairy cell leukemia, which ultimately leads to established standard therapies with optimal outcomes.7


The medication Zelboraf® (vemurafenib) appears active in the treatment of hairy cell leukemia (HCL) according to a report published in New England Journal of Medicine.

A mutation in a gene known as BRAF plays a role in the growth of some cancers, including HCL. Drugs that target BRAF mutations (BRAF inhibitors) can stop or control the growth of HCL.

Researchers conducted a study to evaluate the safety and efficacy of an oral BRAF inhibitor called Zelboraf® (vemurafenib). Specifically, they tested the drug in patients with HCL that had come back or not responded to treatment with drugs known as purine analogues, which interfere with the division and growth of cancer cells.

The trial consisted of two studies—one in Italy (28 patients) and one in the United States (26 patients). Both studies used a 960 mg dose of Zelboraf given twice daily. Patients in Italy received treatment for 18 weeks, and patients in the United States for 16 weeks.

In the Italian study, 96% of patients had a response to Zelboraf (this included partial and complete responses) after eight weeks of treatment. In the U.S. study, 100% of patients had a response after 12 weeks. Rates of complete response (the disappearance of all signs of cancer) were 35% among Italian patients and 42% among U.S. patients.

At a 23-month follow-up, the researchers found that patients in the Italian trial with a complete response had a median relapse-free survival of 19 months, and those with a partial response had a median relapse-free survival of six months. In the U.S. trial, patients with a complete response survived for a median of 25 months without additional treatment, and those with a partial response had a median treatment-free survival of 18 months.

One year after completing treatment, 73% of patients in the U.S. study were alive without disease progression. Overall survival for these patients was 91% at one year.Side effects in both studies were, in general, not severe. Some patients had to receive a reduced dose of Zelboraf due to joint pain and arthritis. A portion of patients (7 out of 50) also developed tumors beneath their skin, which were removed with a simple procedure.

Based on the favorable survival outcomes in these studies, the researchers concluded that Zelboraf appears to be an effective treatment option for patients with HCL that has come back after or has not responded to previous treatment. In addition, the side effects appeared manageable.

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Deoxycoformycin is a drug often used to help decrease symptoms and prolong survival in persons with hairy cell leukemia. A recent study confirms the effectiveness of deoxycoformycin against this rare cancer, and the researchers who conducted the study say that these results are comparable to those of another commonly used drug, called 2-chlorodeoxyadenosine.

Two chemotherapy drugs commonly used as initial treatment for hairy cell leukemia are deoxycoformycin and 2-chlorodeoxyadenosine. Because this cancer is rare, it has been difficult to find enough patients to compare the 2 drugs to each other. Therefore, researchers are not sure as to which drug is the most effective.

Researchers from 32 Spanish treatment facilities reported their results of treating 80 persons with hairy cell leukemia with intravenous deoxycoformycin once per day every 2 weeks for an average of 7 treatments. The findings showed a complete remission (or complete response) in 72% of patients, and partial remission (or partial response) in 16%. The overall response rate was 88%. The average survival time was 46 months, with 49% of those who had a complete response rate expected to be alive and free of disease after 5 years. Relapse (return of the cancer) occurred in 20% of those who had a complete response. Four persons died during treatment; 3 died after the completion of treatment. Treatment with deoxycoformycin was well tolerated, with only 14 persons requiring admission to the hospital during administration of the drug. However, deoxycoformycin does suppress the immune system, which can lead to the development of infections and second cancers. In this group, 2 persons developed herpes and 5 developed a second cancer. It is not known whether the development of these cancers would have occurred, because of the immune effects of the leukemia, without exposure to deoxycoformycin.

The researchers concluded that these findings confirm the effectiveness and acceptable side effects (or limited side effects) of deoxycoformycin in the treatment of persons with hairy cell leukemia. These results appear to be similar to those achieved with 2-chlorodeoxyadenosine.4

Patients with Hairy Cell Leukemia Have an Increased Risk of Second Cancers

Patients with hairy cell leukemia are at an increased risk of developing a second cancer later in their lives.

Researchers affiliated with the National Institutes of Health recently conducted a study to evaluate the risk among patients diagnosed with HCL for developing a second cancer. This study included over 3,100 patients diagnosed with HCL who were followed for 6.5 years.

  • Patients had a 24% increased risk of developing a second cancer compared to the general population.
  • Patients had a six-fold increased risk of Hodgkin’s lymphoma, a five-fold increased risk of non-Hodgkin’s lymphoma, and nearly a 3.6-fold increased risk of thyroid cancer compared with the general population.
  • Patients had a 32% risk of developing a second cancer at 25 years following the diagnosis of HCL.
  • The risk of lung cancer, however, was reduced among patients diagnosed with HCL.

The researchers concluded that patients diagnosed with HCL have a significantly increased risk of developing a second cancer within their lifetime. Patients diagnosed with HCL may wish to speak with their physician regarding their individual risks of specific types of second cancers as well as possible screening and monitoring schedules for the early diagnosis and treatment of second cancers.5

BL22 Immunotoxin Produces High Responses in Hairy Cell Leukemia

Results from an early-phase clinical trial evaluating an innovative form of treatment involving a toxin from bacteria has demonstrated high anti-cancer activity in patients with hairy cell leukemia, as recently reported in the New England Journal of Medicine. These results are consistent with results from preliminary trials evaluating BL22.

Therapy approaches involving biological strategies are emerging as potentially promising treatment options for patients with cancer. BL22, a recombinant immunotoxin, is a novel biological agent currently being evaluated in clinical trials for patients with hairy cell leukemia. BL22 is made up of two different biological components that are fused together through laboratory processes. One component of BL22 is a toxin that is produced by the bacteria species

Pseudomonas. The second component of BL22 is a monoclonal antibody. Monoclonal antibodies are proteins that bind only to specific molecules found on the surface of a particular type of cell. The monoclonal antibody used in BL22 combines with a protein called CD22 that is found specifically on cancerous B-lymphocytes. Once the monoclonal antibody binds to the cancerous cell, the attached Pseudomonas toxin is delivered into the cell and destroys it.

One important aspect of BL22 is that it targets only B-lymphocytes, while sparing healthy cells. This is in stark contrast to chemotherapy or radiation which cause cellular destruction to healthy tissue while producing anti-cancer effects. Often, the side effects caused by chemotherapy or radiation are so severe that treatment scheduling and dosages are affected and only suboptimal regimens can be administered.

Researchers from the National Cancer Institute recently conducted a clinical trial evaluating different doses of BL22 in 16 patients who stopped responding to a standard chemotherapy agent, cladribine. Following treatment, 11 patients achieved complete disappearance of their cancer and 2 patients achieved a partial disappearance of their cancer. The 3 patients who did not respond to treatment had been given low doses of BL22 or had pre-existing antibodies to the toxin. Approximately 16 months following treatment, 3 of the 11 patients achieving complete remission experienced a cancer recurrence. These patients were re-treated with BL22 and all 3 achieved a second complete remission. Side effects caused by the treatment were transient.

These results show very promising anti-cancer effects of BL22 in patients with hairy cell leukemia who have stopped responding to cladribine. The next phase of clinical trials will begin shortly for patients with hairy cell leukemia. Additionally, patients with other forms of leukemia which are CD22 positive are currently being considered for enrollment in these trials. Patients with hairy cell leukemia may wish to speak with their physician about the risks and benefits of participation in a clinical trial evaluating BL22 or other forms of promising biological therapy. 


  1. Tiacci E, Park JH, De Carolis L, et al. Targeting Mutant BRAF in Relapsed or Refractory Hairy-Cell Leukemia. New England Journal of Medicine [early online publication]. September 9, 2015.
  2. ss
  3. Brunangelo F, Enrico T, et al. Simple Diagnostic Assay for Hairy Cell Leukemia by Immunocytochemical Detection of Annexin A1(ANXA1). The Lancet. 2004; 363: 1869-1871.
  4. Cancer, Vol 88, No 2, pp 352-357, 2000.
  5. Hisada M, Chen B, Jaffe E, Travis L. Second cancer incidence and cause-specific mortality among 3,104 patients with hairy cell leukemia: a population-based study. Journal of the National Cancer Institute. 2007; 99: 215-222.
  6.  (New England Journal of Medicine, Vol 345, No 4, pp 241-247, 2001)

  7. Blood, Vol 96, No 9, pp 2981-2986, 2000
  8. Kreitman R, Squires D, Stetler-Stevenson M, et al. Phase I Trial of Recombinant Immunotoxin RFB4(dsFv)-PE38 (BL22) in Patients With B-Cell Malignancies. Journal of Clinical Oncology. 2005; 23: 6719-6729.

  9. American Association for Cancer Research’s annual meeting, New Orleans, March 24-28, 2001).