Osteosarcoma
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(OSA)
- 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:
- Painful swellings of bones in mature individuals (contrast with panosteitis and hypertrophic osteodystrophy)
- 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
- Pulmonary metastases
- Bone metastases
- Juxtacortical (parosteal) origin (vs central/intraosseous above)
- Uncommon
- Arise on extermnal surface of bone
- Surround and attach to cortex
- Have more favourable prognosis