+ 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