(OSA)

Osteosarcoma - canine scapula (Image sourced from Bristol Biomed Image Archive with permission)
Osteosarcoma - radiograph (Image sourced from Bristol Biomed Image Archive with permission)
  • Any malignant neoplasm of mesenchymal origin in which the cells produce osteoid
  • Typically arise in medullary cavity
  • Very uncommon in many species, but most common skeletal neoplasm of dogs and cats
    • Osteosarcoma (80%) > chondrosarcoma (10%) > fibrosarcoma/ haemangiosarcoma (7%)> lymphoid and myeloid tumours of marrow
  • Giant breeds of dog are at massively increased risk
  • Clinical signs:
  • Strong site preference in dogs:
    • Appendicular skeleton 3 or 4 times more frequently involved than axial
    • Metaphyses of proximal humerus, distal radius, distal tibia and distal femur
    • Survival time is a little better for axial than appendicular OSA in dogs
  • In cats - no preferential sites
  • In horses and cattle - mostly in the head
  • Very rare in pigs
  • Classified according to dominant cell types:
    • Osteoblastic
    • Chondroblastic
    • Fibroblastic
    • Undifferentiated
  • Clasified according to radiographic appearance:
    • Osteoblastic
    • Osteolytic
  • Grossly:
    • Grey-white appearance
    • Contain mineralised bone
    • Usually does not penetrate metaphyseal growth plate
  • Microscopically:
    • Variable appearance
    • Neoplastic cells producing osteoid
      • Plump with dark staining nuclei
      • Many mitoses
    • Areas of bone and cartilage formation and fibrosis
  • Prognosis is poor due to early metastasis
  • Juxtacortical (parosteal) origin (vs central/intraosseous above)
    • Uncommon
    • Arise on extermnal surface of bone
    • Surround and attach to cortex
    • Have more favourable prognosis