Malignant histiocytosis

Until recently, malignant histiocytosis was a clearly defined clinical enti ty marked by fever, progressive wasting, lymphadenopathy, hepatosplenomegal y, and pancytopenia. However, for many years the morphologic findings in th is disease continued to cause a great deal of controversy. Now it seems cle ar that most cases of malignant histiocytosis represent anaplastic large ce ll lymphoma (ALCL) with Ki 1 expression, and they are not related to the mo nocyte/macrophage system. This conclusion is based on histopathologic and i mmunohistochemical findings, and more recently, on results from genotypic s tudies. Thus, malignant histiocytosis is a "vanishing disease." (C) 2001 Li ppincott Williams & Wilkins, Inc.