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-induced and fracture-associated OSA

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