Osteosarcoma in dogs

Primary bone neoplasms are relatively common in dogs. Most primary bone tumors in dogs are malignant in that they usually cause death as a result of local infiltration (e.g., pathologic fractures, or extreme pain leading to euthanasia) or metastasis (e.g., pulmonary metastases in osteosarcoma). Neoplasms that metastasize to the bone are rare in dogs; some that occasionally metastasize to bones in dogs are transitional cell carcinoma of the urinary tract, osteosarcoma of the appendicular skeleton, hemangiosarcoma, mammary adenosarcoma, and prostatic adenocarcicoma.

Osteosarcomas (OSA) are the most common primary bone neoplasm in dogs. They can affect either the appendicular or axial skeletons, and they occur primarily in large-breed (and giant-breed) middle age to older dogs. Their biologic behavior is characterized by aggressive local infiltration of the surrounding tissues and rapid hematogenous dissemination (usually to the lungs). Although historically it was believed that osteosarcomas of the axial skeleton had a low metastatic potential, it now appears that their metastatic rate is similar to that of the appendicular osteosarcomas in dogs.

Appendicular osteosarcomas in dogs occur predominantly in the metaphyses of the distal radius, distal femur, and proximal humerus, although other metaphyses can also be affected. As just mentioned, they typically affect male dogs of large and giant breeds, and owners seek veterinary care because of lameness or swelling of the affected limbs. Physical examination usually reveals a painful swelling in the affected area, with or without soft tissue involvement. The pain and swelling can be acute in onset, leading to the presumptive diagnosis of a non neoplastic orthopedic problem and thus considerably delaying diagnosis and definitive therapy for the neoplasm.

The treatment of choice for dogs with osteosarcoma is amputation with adjuvant single-agent or combination chemotherapy. The median survival time in dogs with appendicular osteosarcoma treated with amputation alone is approximately 4 months, whereas in dogs treated with amputation and cisplatin, amputation and carboplatin, or amputation and doxorubicin it is approximately 1 year. The dosages and the recommended ways of administring chemotherapy for dogs with osteosarcoma are ruled by cancer Therapy Protocols. However, the cost of carboplatin therapy is quite high (approximately $3.00 per milligram of drug, or roughly $30.00/kg of body weight).

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