Solid and cystic; loose fascicles of spindle-stellate cells
Pale eosinophilic cytoplasm
Ovoid nuclei with mild atypia; mitotic activity
Collagenous stroma; prominent osteoclast-like multinucleated giant cells; trabeculae of woven bone with osteoblastic rimming
IHC: H3.3 G34W
FISH: USP6-rearrangement