Sections View Full Chapter Figures Tables Videos Full Chapter Figures Tables Videos Supplementary Content ++ DEFINITION ++ This B-lymphocyte malignancy principally involves the marrow and spleen. Blood cytopenias and marrow reticulin fibrosis are frequent features. Irregular cytoplasmic projections on neoplastic B lymphocytes (which gives the disease its name) are most striking when examined as a wet preparation by phase microscopy. ++ EPIDEMIOLOGY ++ It is estimated that about 700 cases per year occur in the United States (approximately 2% of all leukemias). The male-to-female ratio is approximately 4:1. The median age at presentation is approximately 55 years. There is a bimodal peak incidence by age with a mode at approximately age 30 and at age 55. More than 90% of patients are of European descent. Disease is rare in persons of African or Asian descent. ++ ETIOLOGY AND PATHOGENESIS ++ No exogenous causes have been established. A mutation in BRAF (ie, BRAF V600E) is found in virtually all cases. This mutation is not found in cases of variant hairy cell leukemia. Hairy cells are B cells in a late (preplasma cell) stage of development. Neoplastic B cells have clonal immunoglobulin gene rearrangements. Neoplastic B cells express pan-B–cell markers (eg, CD19, CD20, and CD22) and the plasma cell marker prostate cancer antigen-1. Neoplastic B cells express additional surface antigens that are uncommon on B lymphocytes (eg, CD11c, CD25, and CD103). Neoplastic B cells secrete cytokines that may impair normal hematopoiesis (eg, tumor necrosis factor-α). ++ CLINICAL FEATURES ++ Abdominal fullness/discomfort is caused by massive splenomegaly (25%). Fatigue, weakness, and weight loss may occur (25%). Bleeding or infection may be present (25%). Some patients are found incidentally to have abnormal blood count and/or splenomegaly (25%). Painful bony lesions rarely occur (3%). Splenomegaly exists in 90% of patients (median splenic weight approximately 1300 g). Infections with common bacteria, viruses, fungi, Mycobacterium kansasii, Pneumocystis jiroveci, aspergillus, histoplasma, cryptococcus, Toxoplasma gondii or other opportunistic organisms, once common, are less frequent because of more effective initial therapy. Unusual findings include cutaneous vasculitis, leukoclastic angiitis, erythema nodosum, polyarthritis, and Raynaud phenomenon. ++ LABORATORY FEATURES ++ Anemia is present in three-fourths of patients. Eighty percent of patients have absolute neutropenia and monocytopenia. Severe neutropenia (< 0.5 × 109/L) is found in 30% of patients. Severe monocytopenia is hallmark of the disease. Thrombocytopenia occurs in about 75% of patients. Moderate to severe pancytopenia is found in approximately 70% of patients. Careful examination of the blood by light microscopy identifies hairy cells in 80% of patients (Figure 56–1). Liver function test abnormalities occur in 19% of cases, azotemia in 27%, and hyperglobulinemia in 18%, which may be monoclonal. Occasionally, leukocytosis is present as a result of circulating hairy cells. Extreme leukocytosis (> 100 × 109/L) can occur very infrequently, most often seen in the “hairy cell leukemia variant” (see below). Hairy cells comprise less than 20% of lymphocytes in patients with low white blood ... GET ACCESS TO THIS RESOURCE Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth Get Free Access Through Your Institution Contact your institution's library to ask if they subscribe to McGraw-Hill Medical Products. What is MyAccess? Create a FREE MyAccess profile to: Use this site remotely Bookmark your favorite content Track your self-assessment progress and more!