<prompt> Hairy cell leukemia isB cell tumorT cell tumorNK cell tumorAll of above  <response>: Ans. a B cell tumorRef: Harrison 19th ed. 706 Hairy cell leukemia is a B cell tumor disease that presents in older males. Usual presentation involves pancytopenia with splenomegaly. The malignant cells appear to have hairyprojections on light and electron microscopy and show a characteristic staining pattern with tartrate-resistant acid phosphatase. Bone marrow is typically not able to be aspirated, and biopsy shows a pattern of fibrosis. Patients with this disorder are prone to unusual infections, including infection by Mycobacterium avium intracellulare, and to vasculitic syndromes. Hairy cell leukemia is responsive to chemotherapy with interferon , pentostatin, or cladribine, with the latter being the usually preferred treatment. 