A B-cell malignancy that is characterised commonly by symptoms of fatigue, a markedly enlarged spleen, and a distinctive histological appearance on peripheral blood smear and bone marrow biopsy.
The disease is not curable. However, it is highly responsive to therapy and may be managed successfully for a decade or more.
Patients who are without symptoms do not require immediate treatment; early treatment does not extend life expectancy.
In symptomatic patients, purine analogues have largely replaced traditional therapies, such as splenectomy, except in rare cases of splenic rupture or massive splenomegaly.
Supportive care with antibiotics, non-steroidal anti-inflammatory drugs, administration of irradiated blood products, and granulocyte colony-stimulating factors may have a role in therapy for hairy cell leukaemia.
Hairy cell leukaemia (HCL) is an uncommon, indolent, mature B-cell neoplasm. It was described as a distinct clinical entity in 1958.  Seen under the microscope, the cells have delicate cytoplasmic projections, resembling hair, and that is why the disease was named HCL. The disease has a characteristic presentation of pancytopenia, splenomegaly, and circulating hairy cells in blood, marrow, and other haematopoietic organs. 
USF Center for Comparative Effectiveness Research and Evidence Based Medicine
Department of Internal Medicine, College of Medicine
Moffitt Cancer Center & Research Institute, Department of Health Outcomes & Behavior
University of South Florida
AK declares that he has no competing interests.
Division of Hematology-Oncology
Blood and Marrow Transplantation Program
MKD declares that he has no competing interests.
Dr Ambuj Kumar and Dr Mohamed Kharfan-Dabaja would like to gratefully acknowledge Dr Benjamin Djulbegovic, a previous contributor to this topic. BD declares that he has no competing interests.
Section of Haemato-Oncology
Brookes Lawley Institute of Cancer
DC declares that he has no competing interests.
Clinical Professor of Medicine
University of Texas Health Science Center San Antonio
RL declares that he has no competing interests.
Section of Hematology and Oncology
Department of Internal Medicine
Wake Forest University Baptist Medical Center
RC declares that she has no competing interests.
The Royal Marsden Hospital
CD declares that she has no competing interests.
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