Neoplastic disease of the lymphoreticular cells which is considered to be a rare type of chronic leukemia; it is characterized by an insidious onset, splenomegaly, anemia, granulocytopenia, thrombocytopenia, little or no lymphadenopathy, and the presence of hairy or flagellated cells in the blood and bone marrow.

Hairy cell leukemia is an uncommon hematological malignancy characterized by an accumulation of abnormal B lymphocytes. The incidence of hairy cell leukemia (HCL) is 0.28-0.30 cases per 100,000 people in Europe and the United States and the prevalence is 3 cases per 100,000 in Europe with a lower prevalence in Asia, Africa and the Middle East. HCL has an indolent course but with frequent relapses, but with treatment life expectancy is usually the same as that for the general population. HCL was originally described as histiocytic leukemia, malignant reticulosis, or lymphoid myelofibrosis in publications dating back to the 1920s...