SEER is an authoritative source of information on cancer incidence and survival in the United States. SEER currently collects and publishes cancer incidence and survival data from population-based cancer registries covering approximately 28 percent of the U.S. population.
A malignant proliferation of cells showing *Morphologic and immunophenotypic features similar to those of mature tissue histiocytes. *Expression of one or more histiocytic markers without accessory/dendritic cell markers. *Neoplastic proliferations associated with Acute monocytic leukemia are excluded. *Mass of macrophage/mature tissue histiocytic cells occurring in any of several sites.
Rarely, systemic presentation with multiple sites of involvement may be seen, and is sometimes referred to as "malignant histiocytosis".
This is a very aggressive neoplasm with a usually poor response to therapy.