The tumor was composed of relatively uniform round cells with perivascular aggregation, surrounding branching thin-walled vessels (A, ×200, HE staining). The mesenchyma of the tumor showed mucinous degeneration and hyalinization (C, ×400, HE staining). The tumor cells appeared round nuclei, pale eosinophilic cytoplasm (B, ×400, HE staining) and sharply defined cell borders, which was enhanced by PAS staining (D, ×400). Cytological atypia and increased mitotic activity were observed locally (B, ×400, HE staining). HE, hematoxylin and eosin; PAS, periodic acid-Schiff.