Hairy cell leukemia with surface features on monocytes (ruffled membranes at one pole) and lymphocytes. Hairy cell leukemia is an uncommon hematological malignancy characterized by an accumulation of abnormal B lymphocytes. Hairy cell leukemia was originally described as histiocytic leukemia, malignant reticulosis, or lymphoid myelofibrosis in publications dating back to the 1920s. The disease was formally named leukemic reticuloendotheliosis and its characterization significantly advanced by Bertha Bouroncle and colleagues at The Ohio State University College of Medicine in 1958. Its common name, which was coined in 1966, is derived from the "hairy" appearance of the malignant B cells under a microscope.