Pathology: myositis ossificans

Spindle-stellate cells with fascicular-storiform pattern

Abundant pale amphophilic cytoplasm

Round-ovoid nuclei with prominent small nucleoli; occasional mitotic activity

Interspersed "ganglion-like" epithelioid cells; abundant amphophilic cytoplasm; eccentric round-ovoid nuclei with prominent nucleoli and occasional bi-nucleation

Incomplete rim of metaplastic bone; mild chronic inflammatory infiltrate

Spindle-stellate cells with vague fascicular pattern

Abundant pale amphophilic cytoplasm

Round-ovoid nuclei with prominent small nucleoli; occasional mitotic activity

Myxoid-collagenous stroma; seams of osteoid with varialble mineralization; scattered osteoclast-like giant cells

RNA-seq: COL1A1::USP6 gene fusion