Walsh & Hoyt: Histiocytoses

Diseases characterized by accumulation or proliferation of cells of the mononuclear-phagocyte system are generally called reticulohistiocytoses or, simply, histiocytoses. As is the case with the leukemias and the lymphomas, there are several classifications that separate the various types of histiocytosis. The traditional classification is: (a) secondary histiocytoses, which result from chronic infection or an immune disorder; (b) dystrophic or storage histiocytoses, characterized by the systemic or localized storage of either an exogenous or endogenous material; and (c) proliferative histiocytoses, characterized by the uncontrolled proliferation of various cells of the mononuclear-phagocyte system. However, in 1997, The Writing Group of the Histiocytosis Society divided the histiocytic syndromes into three groups: Langerhans cell histiocytoses, benign non-Langerhans cell histiocytoses, and malignant histiocytoses. In this chapter, we use the latter classification and discuss histiocytoses that are neoplastic or have a neoplastic quality.