Fig. 3

a Macroscopic findings of the resected specimen. The tumor consists of a tan red irregular ovoid mass measuring 4.5 × 3.3 × 2.2 cm. b The specimen is stained with hematoxylin-eosin; original magnification: × 20. The specimen is a nodular lesion continuous with the peripheral nerve, characterized by epithelial-like cells with abundant proliferating eosinophilic endoplasmic reticulum forming small clusters. There are a few atypical spindle cells in the background. c Rib bone tissue stained with HE revealing invasion; original magnification: × 4. The specimen is also stained with d S-100, e chromogranin and f synaptophysin; original magnification: × 20