S-100-negative atypical granular cell tumor: report of a case.

A 38-year-old man presented with a solitary, round, 1.2 x 1.2 cm, bluish-colored, dome-shaped, hard nodule on the left side of the neck, which had grown over 2 months (Fig. 1). The nodule was nontender and nonmovable. Light microscopy revealed that the neoplasm was situated in the reticular dermis with extension into the papillary dermis. The tumor showed expansile growth with smooth and round borders, and was made up of sheets of cells arranged in nests or lobules separated by thin delicate connective tissue septa. The tumor cells were round, oval, or polygonal in shape with distinct cellular borders. The cells had abundant eosinophilic granular cytoplasm, and considerable variation of cellular and nuclear size was noted (Fig. 2a). The tumor cell nuclei were vesicular and some had pleomorphism (Fig. 2b). Sometimes multiple nucleoli were seen. Mitoses and necrosis were virtually absent. Immunohistochemical staining revealed that some of the cytoplasmic granules stained positively with periodic acid-Schiff (PAS) after diastase treatment. Tumor cells showed strong reactivity for CD68 and neuron-specific enolase, and negative results for S-100, factor XIIIa, cytokeratin, desmin, CD34, and smooth muscle actin. Electron microscopy revealed that the tumor was composed of polygonal cells with round to irregular nuclei, and the cytoplasm contained numerous secondary lysosomes. The tumor was completely excised.