Fig. 1

a The tumor (right) is extending to the mucosa (Hematoxylin-eosin, original magnification ×40). b Tumor cells are arranged in pseudoalveolar pattern. An osteoclast-like giant cell is also present. (Hematoxylin-eosin, original magnification × 200). c The cells are polygonal in shape with variable amount of eosinophilic to clear cytoplasm. Characteristic osteoclast-like giant cells are dispersed in between. (Hematoxylin-eosin, original magnification × 400). d Strong and diffuse S100 protein staining. (Original magnification × 200). e FISH analysis using dual-color, EWSR1 breakapart probe. The tumor cells show one fusion signal pattern, one green and two red, indicative of a rearrangement of one copy of EWSR1 region