The excised mass measured 0.4 × 0.5 cm at its base and 1.0 cm in height (Figure, B). Microscopically, a mass of grouped, large epithelioid histiocytes (Figure, C) began beneath a mildly parakeratotic epidermis and a narrow band of collagen; they were usually mononucleated but occasionally multinucleated, subdivided by fine collagen strands, and accompanied by a mixture of lymphocytes, polymorphonuclear leukocytes, and eosinophilic leukocytes. The tumor evinced incursion into the orbicularis muscle and tarsus (Figure, B). The principal polygonal cells were endowed with abundant eosinophilic or amphophilic cytoplasm (Figure, D) without periodic acid–Schiff–positive inclusions. Their nuclei were round and possessed small nucleoli; mitotic figures were not identified. Acid fast and methenamine silver stains did not detect organisms. The large tumor cells were strongly positive for vimentin (Figure, E), sporadically positive for S-100 protein, strongly positive for CD163, and more weakly positive for CD68 (Figure, F) and α1-antitrypsin. Staining results for lysozyme, factor XIIIa, and AE1/AE3 (for keratin), HMB-45, melan A, and Mitf (for melanocytes), desmin and smooth muscle actin (for myoid cells), and CD1a (for Langerhans cells) were negative in the principal tumor cells. Ki-67 nuclear staining for cells in S-phase was absent in the round cells but present among the dispersed inflammatory cells.