ABSTRACT
Introduction 471 Clinical and laboratory findings 471 Sites of involvement and morphologic features 472 Peripheral blood 472 Bone marrow 472 Spleen and other tissues 473 Diagnostic tools 473 Tartrate-resistant acid phosphatase activity 473 Immunophenotyping 473 Differential diagnosis 473 Differentiating between hairy cell leukemia and 474
HCL-like disorders
Monitoring of minimal residual disease 475 Biologic features of hairy cell leukemia cells 475 Cellular origin and pathogenesis of HCL 475 Adhesion and homing properties of hairy cell leukemia cells 475 Bone marrow fibrosis 476 Hairy morphology 476 Monocyte-macrophagic properties of hairy cell 476
leukemia cells Open questions and future directions 477 Key points 477 References 478
Hairy cell leukemia (HCL) is an unusual B cell chronic lymphoproliferative disorder that was first described as Leukämische reticuloendotheliose by Ewald in 1923.1 More than 30 years later, Bouroncle identified HCL as a distinct disease entity.2 Although the biology, pathogenesis and etiology of HCL are still poorly understood, remarkable progress has been made over the past 50 years in diagnosis and therapy of this pathologic entity.
