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Hairy cell leukemia is an uncommon neoplastic disorder of B lymphocytes that has a much higher prevalence in men than in women. The patient usually presents with bicytopenia or pancytopenia. Absolute neutropenia and monocytopenia are nearly constant features. The blood and marrow biopsy contain hairy cells, which are lymphocytes that have prominent cytoplasmic projections and give the disease its name. Splenomegaly, sometimes massive, is a nearly constant feature. The liver and abdominal lymph nodes may be enlarged. The immunophenotype of the hairy cells, CD11c+, CD19+, CD20+, CD22+, CD25+, and CD103+, confirms the diagnosis. Disease complications include standard or opportunistic infections. Approximately 10 percent of patients may not require immediate treatment. For patients requiring treatment, cladribine is the drug of choice because of the very high complete remission rate and prolonged duration of remission in a high proportion of patients. Pentostatin also is effective in this disease. Interferon-α, rituximab, anti-CD22 recombinant immunotoxin (BL22), or splenectomy can be useful in selected patients unresponsive to cladribine or pentostatin. The patient with hairy cell leukemia can expect a very long duration of survival with current therapy. The 5-year event-free survival rate after treatment is approximately 90 percent of patients initially treated with cladribine.

Acronyms and Abbreviations

Acronyms and abbreviations that appear in this chapter include: DFS, disease-free survival; G-CSF, granulocyte colony-stimulating factor; HCL, hairy cell leukemia; HCLv, hairy cell leukemia variant; IL, interleukin; MRD, minimal residual disease; SMZL, splenic marginal zone lymphoma; TRAP, tartrate-resistant acid phosphatase.

Hairy cell leukemia (HCL) is an uncommon chronic lymphoproliferative disorder characterized by circulating B lymphocytes that display prominent cytoplasmic projections. The neoplastic B cells infiltrate the marrow and spleen. Afflicted individuals often are males who present with bicytopenia or pancytopenia, splenomegaly, or recurrent, serious infections. In 1958, Bouroncle and colleagues1 recognized the disorder as a distinct clinicopathologic entity and referred to it as leukemic reticuloendotheliosis. Eight years later, Schreck and colleagues2 reported on the same disease, describing “peculiar cells that had numerous short villi on phase contrast microscopy, which they referred to as ‘hairy cells.’” The disease designation hairy cell leukemia has since gained official recognition. In 1972, Giblett and colleagues3 made the seminal observation that one-third of children with severe combined immunodeficiency syndrome were deficient in the purine catabolic enzyme adenosine deaminase. Adenosine deaminase catalyzes the irreversible deamination of adenosine to inosine and of 2′-deoxyadenosine to 2′-deoxyinosine. Cohen and investigators4 reported that the intracellular accumulation of deoxyadenosine triphosphate was responsible for the lymphopenia seen in severe combined immune deficiency. Later, Carson and colleagues5 reported that 2-chlorodeoxyadenosine (cladribine), a chlorine-substituted purine deoxynucleoside, was the most potent among a panel of substituted purine analogues screened for in vitro cytotoxicity. In 1990, investigators at Scripps Clinic, La Jolla, California, first reported on 12 patients with HCL treated with a single 7-day course of cladribine administered at 0.1 mg/kg per day by continuous intravenous infusion.6 Of the ...

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