Resource Library: Osteosarcoma, Canine

OSTEOSARCOMA, CANINE
Osteosarcoma is a tumor of the bone and is the most common primary bone tumor in the dog. It typically affects middle-aged to older large breed dogs with a peak in incidence seen at seven years of age. More than 75% of osteosarcomas develop in the long bones of the skeleton.

Lameness that is increasing in severity is the most common symptom when a dog develops bone cancer. There may be swelling localized swelling in the affected leg There may be a history of intermittent lameness that becomes progressively worse. If the ribs are affected, a palpable, painful mass may be present. Osteosarcomas tend to spread to the lungs, but breathing difficulty may not develop for months. Decreased appetite and decreased activity levels are additional signs.

Diagnosis is includes a complete physical exam and radiographs of the affected limb and lungs . There will typically be a lytic lesion with loss of normal bone structure and density. A bone biopsy can confirm the tumor type but is not always necessary..

Surgery (amputation or limb sparing surgery) is the first line of treatment for canine osteosarcomas. Prior to performing surgery staging is recommended. Staging is a procedure to determine if the cancer has spread and ensure that all other major organ systems are functioning adequately. These tests include a complete blood count, serum chemistry analysis, and chest x-rays. Osteosarcomas often spread to the lungs. If there is any evidence of tumor spread to the lungs the prognosis is less favorable (median survival times of 2 months are reported). Any tissue removed at surgery is submitted for pathologic evaluation for identification.

Successful treatment includes control of the primary tumor as well as prevention of metastasis. A accepted treatment for osteosarcoma of is amputation of the affected limb. Even large and giant breeds can function well after limb amputation and most owners are pleased with their dog's mobility and quality of life after this surgery. Following amputation, chemotherapy is recommended to decrease the chance of early failure due to lung metastasis. Without chemotherapy, amputation alone is considered palliative to minimize pain (which can be very severe with these tumors) and improve quality of life. Once tumors develop in the lungs there are less options for treatment. The median survival time with surgery followed by chemotherapy is approximately 12 months.

With no treatment there is increasing and often severe pain in the affected leg that quickly becomes becomes non-responsive to pain medications. Other therapies include limb sparing to remove the tumor at a local site and spare the limb with an internal prosthesis or stereotactic radiation to eliminate the tumor locally and spare the limb. These patients should undergo chemotherapy after surgery or radiation to maximize the survival after the limb sparing. Failure to do so will not increase survival when compared to amputation alone and the cost is considerably more.

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