Hairy Cell Leukemia

What is Hairy Cell Leukemia?

Hairy cell leukemia is a mature B cell neoplasm. It is usually classified as a sub-type of chronic lymphoid leukemia for convenience. It is uncommon, representing about 2% of all leukemias, or less than a total of 2000 new cases diagnosed each year in North America and Western Europe combined.

Originally known as histiocytic leukemia, malignant reticulosis, or lymphoid myelofibrosis in publications dating back to the 1920s, this disease was formally named leukemic reticuloendotheliosis and its characterization significantly advanced by Bertha Bouroncle, M.D. and her colleagues at the Ohio State University College of Medicine in 1958. Its common name, which was coined in 1966, is derived from the appearance of the cells under a microscope.

When not further specified, the "classic" form is often implied. However, two variants have been described: Hairy cell leukemia-variant, which usually is diagnosed in men and a Japanese variant. The non-Japanese variant is more difficult to treat than either 'classic' HCL or the Japanese variant HCL.

This disease is rare, with fewer than 1 in 10,000 people being diagnosed with HCL during their lives. Men are four to five times more likely to develop hairy cell leukemia than women. In the United States, the annual incidence is approximately 3 cases per 1,000,000 men each year, and 0.6 cases per 1,000,000 women each year. It is less common in people of African and Asian descent compared to people of European descent.

It does not appear to be hereditary, although occasional familial cases that suggest a predisposition have been reported, usually showing a common HLA type.

Hairy cell leukemia-variant

Hairy cell leukemia-variant, or HCL-V, is usually described as a prolymphocytic variant of hairy cell leukemia. It was first formally described in 1980 by a paper from the University of Cambridge's Hayhoe lab. About 10% of HCL patients have this variant form of the disease, representing about 60-75 new HCL-V patients each year in the U.S. While classic HCL primarily affects men, HCL-V is somewhat more evenly divided between males and females. While the disease can appear at any age, the median age at diagnosis is over 70.

Similar to B-PLL in Chronic Lymphocytic Leukemia, HCL-V is a more aggressive disease. It is less likely to be treated successfully than classic HCL and remissions tend to be shorter. Many treatment approaches, such as Interferon-alpha, CHOP and common alkylating agents like cyclophosphamide provide very little benefit.) to interfere with bone marrow biopsies; and

  • Low or no expression of CD25 (also called the Interleukin-2 receptor alpha chain or p55) on cell surfaces.

The lack of CD25, which is part of the receptor for a key immunoregulating hormone, may explain why HCL-V cases are normally resistant to treatment by immune system hormones.

HCL-V, which has a high proportion of hairy cells without a functional p53 tumor suppressor gene, is somewhat more likely to transform into a higher-grade disease, with Daniel Catovsky suggesting a typical transformation rate of 5% in the U.K., which is similar to the Richter's transformation rate for SLVL and CLL Among HCL-V patients, the most aggressive cases normally have the least amount of p53 gene activity. Hairy cells without the p53 gene tend, over time, to displace the less aggressive p53+ hairy cells.

Hairy cell leukemia-Japanese variant

Hairy cell leukemia-Japanese variant or HCL-J. There is also a Japanese variant, which is more easily treated. Treatment with cladribine has been reported.

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Hairy Cell Leukemia Symptoms

In hairy cell leukemia, the broken "hairy cells" build up in the bone marrow, which means that the bone marrow has difficulty producing enough normal cells: white blood cells to fight infections, red blood cells to carry oxygen, and platelets to stop bleeding. Consequently, patients usually present with infection, anemia-related fatigue, and/or easy bleeding.

Most symptoms are often vague, such as "persistent fatigue" or "not feeling well." Some of the leukemic cells may gather in the spleen and cause it to swell; this can have the side effect of making the person feel full even when he or she has not eaten much.

Hairy cell leukemia is commonly diagnosed after a routine blood count shows unexpectedly low numbers for one or more kinds of blood cells, or after unexplained bruises or unexplained infections, such as repeated bouts of pneumonia in an otherwise apparently healthy patient.

Platelet function may be somewhat impaired in HCL patients, although this does not appear to have any significant practical effect. It may result in somewhat more mild bruises than would otherwise be expected for a given platelet count or a mildly increased bleeding time for a minor cut. It is likely the result of producing slightly abnormal platelets in the overstressed bone marrow tissue.

Patients with a high tumor burden may also have somewhat reduced levels of cholesterol, especially in patients with an enlarged spleen. Cholesterol levels return to more normal values with successful treatment of HCL.

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Hairy Cell Leukemia Cause

The cause is unknown, but it is generally accepted that it is not caused by tobacco, ionizing radiation, or industrial chemicals other than possibly diesel. Farming and gardening appear to increase the risk in some studies. The possibility that HCL is caused by a random accident during routine cell division can not be ruled out.

With respect to compensation for veterans exposed to Agent Orange and other pesticides, the US Institute of Medicine announced "sufficient evidence" of an association between exposure to herbicides and later development of chronic B-cell leukemias and lymphomas in general.

The IOM report emphasizes that neither animal nor human studies indicate that exposure to this herbicide is associated with or connected to HCL specifically, or that data supports even claims of biological plausibility.

The IOM committee is instead applying data from chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL) to draw conclusion about HCL, saying that it "sees no reason to exclude HCL or any other chronic hematoproliferative diseases of B-cell origin lacking its own specific epidemiologic evidence".

As a result of the IOM's decision to lump HCL in with other B-cell leukemias and lymphomas, the US Department of Veterans Affairs listed HCL as an illnesses presumed to be a service-related disability.

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Hairy Cell Leukemia Diagnosis

The diagnostic path may have begun with a simple test like a complete blood count (also called a ''full blood count''), but this is not adequate to diagnose HCL. A CBC normally shows low counts for white blood cells, red blood cells, and platelets in HCL patients. However, if large numbers of hairy cells are in the blood stream, then normal or even high lymphocyte counts may be found.

On physical exam, 80–90% of patients display splenomegaly, which can be massive. (CD103, CD22, and CD11c are strongly expressed.)

Hairy cell leukemia-variant (HCL-V), which shares some characteristics with B cell prolymphocytic leukemia (B-PLL), does not show CD25 (also called the Interleukin-2 receptor, alpha). As this is relatively new and expensive technology, its adoption by physicians is not uniform, despite the advantages of comfort, simplicity, and safety for the patient when compared to a bone marrow biopsy. The presence of additional lymphoproliferative diseases is easily checked during a flow cytometry test, where they characteristically show different results.

The differential diagnoses include: several kinds of anemia, including myelophthisis and aplastic anemia, and most kinds of blood neoplasms, including hypoplastic myelodysplastic syndrome, atypical chronic lymphocytic leukemia, B-cell prolymphocytic leukemia, or idiopathic myelofibrosis.

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Hairy Cell Leukemia Pathophysiology

Pancytopenia in HCL is caused primarily by marrow failure and splenomegaly. Bone marrow failure is caused by the accumulation of hairy cells and reticulin fibrosis in the bone marrow, as well as by the detrimental effects of dysregulated cytokine production. They may be related to pre-plasma marginal zone B cells or memory cells.

Cytokine production is disturbed in HCL. Hairy cells produce and thrive on TNF-alpha. It has not yet been demonstrated that any of these changes have any practical significance to the patient.

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