DERMATOFIBROMA - SUPERFICIAL FIBROUS PROLIFERATION WITH REACTIVE HISTIOCYTES A MULTIPLE IMMUNOSTAINING ANALYSIS

Background. Dermatofibroma (DF) is a superficial form of benign fibrou s histiocytoma, composed of a mixture of fibroblastic cells and histio cytic cells. The histogenesis of this lesion is a matter of controvers y. Methods. Forty-five cases of DF were investigated by single and mul tiple immunostaining techniques, using panel of 12 antibodies includin g proliferating cell nuclear antigen (PCNA), vimentin, and macrophage/ histiocyte markers (HAM56 and CD68). Results. Double immunostaining de monstrated that 58% of the DF cells simultaneously expressed PCNA and vimentin, whereas only 5% were PCNA(+)/HAM56(+), and 2% were PCNA(+)/C D68(+). By triple-stain for PCNA, vimentin, and HAM56, 56% of the DF c ells were PCNA(+)/ vimentin(+)/HAM56; but only a few cells were PCNA()/ HAM56(+)/vimentin(+/-). Of the PCNA positive cells, 88% were viment in(+) HAM56(-) and 10% were HAM56(+) vimentin(-/+). The cells positive for CD68 showed similar distribution to that of HAM56(+) cells, thoug h there were fewer of the former than the latter in most cases. These results suggest that the majority of the proliferating cells in DF exp ress vimentin but not histiocytic markers. Morphologically, the PCNA()/vimentin(+)/HAMS6(-) (or CD68(-)) cells exhibited a spindle-shaped c onfiguration resembling fibroblasts, whereas most of the HAM56(+)/CD68 (+) cells possessed abundant rounded cytoplasm and were similar to nor mal histiocytes. Conclusions. The present study suggests that the prol iferative compartment of DF cells is composed chiefly of mesenchymal/f ibroblastic lineage, accompanied by varying numbers of normal reactive histiocytes.