Pathology: extraskeletal osteosarcoma

Sheets and fascicles of polygonal-spindle cells

Pale amphophilic cytoplasm

Round-ovoid nuclei with macronucleoli, and marked pleomorphism; conspicuous mitotic activity

Foci of osteoid and chondroid deposition

Haemorrhagic cyst-like spaces with multinucleated giant cells

Sheets of polygonal-spindle cells

Pale amphophilic cytoplasm

Round-ovoid nuclei with hyperchromasia and marked pleomorphism; conspicuous mitotic activity

So-called "malignant" osteoid