Hairy cell leukemia

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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[1], 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,[2] 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.

Hairy cell leukemia-variant, or HCL-V, is usually described as a prolymphocytic variant of hairy cell leukemia.[3] It was first formally described in 1980 by a paper from the University of Cambridge’s Hayhoe lab.[4] 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.[5] While the disease can appear at any age, the median age at diagnosis is over 70.[6]

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.[5] Pentostatin and cladribine provide some benefit to many HCL-V patients, but with shorter remissions and lower response rates compared to classic HCL. More than half of patients respond partially to splenectomy.[5]

In terms of B cell development, the prolymphocytes are less developed than lymphocyte cells or plasma cells, but are still more developed than their lymphoblastic precursors.

HCL-V differs from classic HCL principally in these respects:

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.[9]

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