OSTEOSARCOMA
+ General Considerations
- Appendicular bone tumors are rare in cats and account for 0.5% of all feline tumors
- 67%-90% are malignant with OSA the most common primary bone tumor (70%-80%), then FSA and CSA
- FSA is the 2nd most common primary bone tumor in the cat followed by CSA and HSA
- HSA rarely affects bones of cats
- Biologic behaviour is largely unknown although metastases have been reported with CSA and HSA
- 62% skeletal OSA and 38% extraskeletal OSA
- Site predilection: 55%-67% appendicular and 33%-44% axial
- Appendicular sites: proximal humerus, distal femur, and proximal tibia
- Primary appendicular bone tumors are more common in the diaphysis than metaphyseal areas and the pelvic limb (50%) is more frequently affected than thoracic limb sites (30%)
- Feline appendicular OSA is less aggressive than canine appendicular OSA with a slower growth and metastasis less common and occurring later in the course of disease
- Juxtacortical and extraskeletal OSA common in the cat
- 80% of extraskeletal OSA occur in subcutaneous tissue and 54% in the interscapular region (i.e., VAS)
- 1 report each of radiation-in
Clinical Features
+ Signalment
- Mean age 8.5-10.2 years (range, 1-20 years)
- Axial OSA presents at a significantly older age than appendicular OSA (8.0 years v 10.4 years)
- No sex predisposition ± males
+ Survey Radiographs
- Regional radiographic findings are similar to dogs, but lesions arising from the periosteal surface and osteolytic lesions are more common in appendicular skeleton (80%)
- Intramedullary OSA more common with axial OSA
- Pulmonary metastases are rarely diagnosed
+ Histopathology
- Histologic features: mesenchymal cells embedded in malignant osteoid although cartilage may be abundant, osteoid scant, and multinucleate giant cells common
- Invasive tumor ± soft tissue compression rather than infiltration
- Chondroblastic, fibroblastic, telangiectatic, and giant-cell subtypes have been described but are not prognostic
+ Treatment
Amputation alone without chemotherapy may be curative in cats with appendicular OSA
+ Prognosis
- MST 24-49 months for appendicular OSA is commonly cited, but mean survival time 11.8 months recently reported
- Mean survival time 5.5-6.1 months for axial OSA, with a significantly poorer prognosis due to increased difficulty with local disease control
- Mean survival time 12.7 months for extraskeletal OSA