Fascin and the differential diagnosis of childhood histiocytic lesions.

This is a descriptive screening of 46 examples of childhood histiocytic lesions and some of their look-alikes using a monoclonal antibody, p55, to fascin. Fascin, an actin-bundling protein, identifies dendritic cells in the blood and in tissues. Our aim was to test the diagnostic utility of the antibody in various lesions at different sites and to see whether the staining patterns give insight into the cell types involved. Fascin intensely stained the cells of juvenile xanthogranulomas (JXG), Rosai-Dorfman lesions, and soft tissue dendrocytomas. Normal Langerhans' cells and the cells of Langerhans' cell histiocytosis were unreactive. Their lack of fascin staining may be relevant to fascin being maturation as well as lineage related. Epithelioid and palisading granulomas were unstained, though an example of Kikuchi lymphadenitis had large numbers of dendritic-type cells that stained strongly. A reticulohistiocytoma of the skin was also unstained and look-alike lesions, Spitz nevi, and mast cell lesions did not stain. Two of three large-cell lymphomas (both CD30+) also had fascin reactivity. Even though fascin is not specific to dendritic cells, staining other cell types as well (false positive), and not entirely sensitive, dendritic cells such as tissue Langerhans' cells are unstained (false negative), there seems to be a consistency of staining in childhood histiocytic lesions. This may be of diagnostic use when read in the context of the tissue differential diagnosis. Whether fascin can serve as a marker for the dendritic cell lineage, or at least for some phases of dendritic cell lifecycle, is not answered by this survey.