Appendicular Osteosarcoma in Dogs

Clinical Presentation

Appendicular (legs) osteosarcoma (OSA-bone sarcoma) is most common in giant and large breed dogs, with an average age of onset of 7 years. The most common site of development of OSA is the distal radius (near the wrist), followed by the proximal humerus (near the shoulder) and less commonly proximal and distal femur and tibia (hips to ankles). While acute lameness due to pathologic fracture (disease-related bone break) occurs in some dogs, most present with a history of progressive lameness over several weeks.

Diagnostic Tests

The hallmark x-ray changes of bony neoplasia (cancer) are bone lysis (disintegration), varying degrees of changes to the tissue surrounding the bone, loss of detail in bone and extension into the soft tissue. This latter effect is known as Codman's triangle or a “sunburst” effect.

Chest x-rays (3 views) are recommended prior to surgery to rule out metastatic (spread) disease in the lungs. Less than 10% of dogs have radiographic evidence of pulmonary metastasis (spread to the lungs) at the time of presentation.

Bone scintigraphy (bone scan or nuclear scan) is a helpful diagnostic procedure to rule out metastatic disease to bone; however, fewer than 3% of patients have bony metastases at the time of presentation.

Bone biopsy may be performed prior to initiating treatment to confirm the diagnosis. Surgery is often performed without a bone biopsy as most dogs with OSA are very painful and have “classic” x-ray changes on the leg.

Surgical Options

Amputation remains the treatment of choice to alleviate pain, improve quality of life and control the primary tumor. In our experience, greater than 95% of pet owners report good to excellent quality of life following leg amputation. Severe pre-existing arthritis is the primary limiting factor in proceeding with amputation. We routinely place the patient's affected leg a sling and then walk them around exam room for several minutes so that the pet owner can develop a comfort level with their pet's ability to ambulate on 3 legs.

Limb or leg sparing surgery remains an important option for giant breed dogs with OSA of the distal radius. Good to excellent leg function is reported by 80% of pet owners.

Chemotherapy Options and Survival Statistics

Cisplatin, carboplatin and doxorubicin (adriamycin) have all shown benefit in the treatment of appendicular OSA. Chemotherapy is initiated as soon after amputation as the health status of the patient will allow.

Cisplatin has been described historically as the chemotherapeutic of choice, but has the disadvantage of requiring hospitalization for fluid therapy to prevent nephrotoxicity (kidney damage). The average survival time after surgery and 4 treatments of cisplatin is 11 months.

Carboplatin is a newer platinum based drug that is replacing cisplatin in popularity. It is well tolerated with minimal gastrointestinal side effects. Myelosuppression (bone marrow suppression) is the major dose limiting toxicity, with the peak occurring 2 weeks after administration. At least 4 treatments, administered at 3-week intervals, are recommended. The average survival time after surgery is 9 months.

Doxorubicin is an alternative to the platinum based drugs. It is overall better tolerated than cisplatin, but the incidence of gastrointestinal side effects is higher than with carboplatin. Published studies indicate that 10% of large and giant breed dogs treated with doxorubicin develop cardiomyopathy (heart disease). The primary reason for treating dogs with doxorubicin instead of platinum-based drugs (cisplatin and carboplatin) is cost. Five treatments of doxorubicin can be administered for the same price as one carboplatin treatment. Unfortunately, this approach is less effective than the platinum drugs. The average survival time with surgery is 7 months.

The combination of cisplatin and doxorubicin has been found to have the longest survival time, an average post-amputation of 18 months. The dose of each of the medications is reduced to help lessen the side effects.

Palliation

Radiation therapy and/or the use of non-steroidal anti-inflammatory medications (NSAIDs) can be used to reduce bone pain and improve quality of life when the pet owner decides against surgery and chemotherapy.

Piroxicam (feldene) is the NSAID of choice for alleviating bone pain and is given orally once daily.

Radiation therapy is the most effective bone pain reliever. Typically, 3 treatments are administered on days 0, 7 and 21 (time span equals one month). Pain is controlled for 2-6 months. Palliation is less effectively achieved when the tumor is located in the proximal humerus.

Metastatic Disease

Dogs diagnosed with metastatic disease have an average survival time of 2 months. Chemotherapy is ineffective at this stage. Surgery for pulmonary metastases is considered in patients with no more than 2 nodules that develop greater than 300 days after initial diagnosis. Average remission time after surgery in this setting is 4.2 months. Chemotherapy may be recommended following the surgery to remove pulmonary metastases, but it is unknown at this time if survival times are improved, as this combination treatment for metastatic disease has yet to be evaluated in dogs.