Pathology: osteosarcoma, conventional

Osteosarcoma, conventional, osteoblastic

  • Sheets of polygonal cells

  • Amphophilic cytoplasm

  • Round-ovoid nuclei with marked pleomorphism; brisk mitotic activity

  • Delicate seams and sheets of osteoid with variable mineralization

Osteosarcoma, conventional, chondroblastic

  • Sheets of polygonal cells

  • Eosinophilic cytoplasm

  • Round-ovoid nuclei with marked pleomorphism; brisk mitotic activity

  • Prominent hyaline cartilage matrix; seams-sheets of osteoid with variable mineralization; focal osteoblastic differentiation

Osteosarcoma, conventional, chondroblastic

  • Sheets of polygonal cells

  • Eosinophilic cytoplasm

  • Round-ovoid nuclei with marked pleomorphism; brisk mitotic activity

  • Prominent hyaline cartilage matrix; seams-sheets of osteoid with variable mineralization; focal osteoblastic differentiation

Osteosarcoma, conventional, fibroblastic

  • Spindle-polygonal cells with storiform-fascicular pattern

  • Eosinophilic cytoplasm

  • Ovoid nuclei with occasional multinucleation and marked pleomorphism; conspicuous mitotic activity

  • Secondary aneurysmal cyst formation; osteoid* with mineralization

* Osteoid may be very focal necessitating extensive sampling for definitive classification

Osteosarcoma, conventional, epithelioid

  • Sheets of epithelioid cells

  • Amphophilic cytoplasm

  • Round-ovoid nuclei with macronucleoli and moderate pleomorphism; mitotic activity

  • Delicate seams of osteoid with variable mineralization; focal chondroid differentiation; ectatic and branching vasculature

  • IHC: SATB2

Osteosarcoma, conventional, giant cell-rich

  • Sheets of polygonal cells

  • Amphophilic cytoplasm

  • Round-ovoid nuclei with small nucleoli and moderate pleomorphism; mitotic activity

  • Prominent osteoclast-type giant cells; seams and sheets of osteoid with mineralization

Osteosarcoma, conventional, giant cell-rich

  • Sheets of epithelioid cells

  • Amphophilic cytoplasm

  • Round-ovoid nuclei with prominent nucleoli and moderate pleomorphism; mitotic activity

  • Prominent osteoclast-type giant cells; seams and sheets of osteoid with minimal mineralization