Fig. 3

Photomicrographs of pathological specimens: a Compact spindle cells with rod-shaped nuclei and dense pericellular reticulin were aligned (Antoni A regions; hematoxylin and eosin; original magnification × 200; scale bar = 200 µm). We observed whorl formation in this area. b Stellate and spindle cells with smaller and hyperchromatic nuclei and scanty surrounding reticulin arranged in a myxoid stroma (Antoni B regions; hematoxylin and eosin; original magnification × 200; scale bar = 100 µm). c Tumor cells were stained with Ki-67 (original magnification × 200; scale bar = 100 µm). This area shows mitotic features with a Ki-67 index of 10–20%. d Tumor cells were diffusely positive for S100 (original magnification × 200; scale bar = 200 µm)