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| ==Classification== | | ==Classification== |
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| ===Hairy cell leukemia-variant===
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| '''Hairy cell leukemia-variant''', or HCL-V, is usually described as a prolymphocytic variant of hairy cell leukemia.<ref>{{cite web |url=http://bloodjournal.hematologylibrary.org/cgi/content/abstract/76/1/157 |title=A variant form of hairy cell leukemia resistant to alpha-interferon: clinical and phenotypic characteristics of 17 patients -- Sainati et al. 76 (1): 157 -- Blood |accessdate=2007-09-10 |format= |work=}}</ref> It was first formally described in 1980 by a paper from the University of Cambridge's Hayhoe lab.<ref name="pmid7206776">{{cite journal |author=Cawley JC, Burns GF, Hayhoe FG |title=A chronic lymphoproliferative disorder with distinctive features: a distinct variant of hairy-cell leukaemia |journal=Leuk. Res. |volume=4 |issue=6 |pages=547-59 |year=1980 |pmid=7206776 |doi=}}</ref> 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.<ref name="pmid11243388">{{cite journal |author=Matutes E, Wotherspoon A, Brito-Babapulle V, Catovsky D |title=The natural history and clinico-pathological features of the variant form of hairy cell leukemia |journal=Leukemia |volume=15 |issue=1 |pages=184-6 |year=2001 |pmid=11243388 |doi=}}</ref>
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| Similar to B-PLL in [[Chronic Lymphocytic Leukemia]], HCL-V is a more aggressive disease which is harder to treat successfully than classic HCL. Many treatment approaches, such as Interferon-alpha, CHOP and common alkylating agents like cyclophosphamide provide very little benefit.<ref name="pmid11243388"> </ref> 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.<ref name="pmid11243388"> </ref>
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| 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.
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| HCL-V differs from classic HCL principally in these respects:
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| * High white blood cell counts, sometimes in excess of 100,000 cells per microliter;
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| * More aggressive course of disease that requires more frequent treatment;
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| * Cells with an unusually large nucleolus for their size;
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| * Little excess fibronectin (which is produced by classic hairy cells<ref>{{cite web |url=http://bloodjournal.hematologylibrary.org/cgi/content/abstract/83/2/497 |title=The bone marrow fibrosis of hairy-cell leukemia is caused by the synthesis and assembly of a fibronectin matrix by the hairy cells -- Burthem and Cawley 83 (2): 497 -- Blood |accessdate=2007-09-10 |format= |work=}}</ref>) to interfere with bone marrow biopsies; and
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| * Low or no expression of CD25 (also called the Interleukin-2 [IL-2] receptor alpha chain or p55) on cell surfaces.<ref>{{cite web |url=http://bloodjournal.hematologylibrary.org/cgi/content/abstract/82/2/528 |title=Phenotypic analysis of hairy cell leukemia: "variant" cases express the interleukin-2 receptor beta chain, but not the alpha chain (CD25) -- de Totero et al. 82 (2): 528 -- Blood |accessdate=2007-09-10 |format= |work=}}</ref>
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| 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.<ref>{{cite web |url=http://bloodjournal.hematologylibrary.org/cgi/content/abstract/76/1/157 |title=A variant form of hairy cell leukemia resistant to alpha-interferon: clinical and phenotypic characteristics of 17 patients -- Sainati et al. 76 (1): 157 -- Blood |accessdate=2007-09-10 |format= |work=}}</ref>
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| 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 transformation rate of 5% in the U.K., which is similar to the Ricther's transformation rate for SLVL and CLL.<ref name="pmid11243388"> </ref> Among HCL-V patients, the most aggressive cases normally have the least amount of p53 gene activity.<ref name="pmid10576509">{{cite journal |author=Vallianatou K, Brito-Babapulle V, Matutes E, Atkinson S, Catovsky D |title=p53 gene deletion and trisomy 12 in hairy cell leukemia and its variant |journal=Leuk. Res. |volume=23 |issue=11 |pages=1041-5 |year=1999 |pmid=10576509 |doi=}}</ref> Hairy cells without the p53 gene tend, over time, to displace the less aggressive p53+ hairy cells.
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| ===Hairy cell leukemia-Japanese variant===
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| '''Hairy cell leukemia-Japanese variant''' or HCL-J. There is also a Japanese variant, which is more easily treated.
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| ==References== | | ==References== |