Hypo- to moderately cellular spindle cell fascicles
Pale eosinophilic cytoplasm with delicate tapering processes
Hyperchromatic ovoid nuclei with mild pleomorphism; inconspicuous mitotic activity
Abundant interspersed collagenous stroma
Broad anastomosing woven bone trabeculae with "scaffolding" on preexisting bone; patchy necrosis
FISH: MDM2 amplification