Bone Cancer in Dogs
Osteosarcoma (OSA) is a malignant tumor arising from bone cells. It the most common type of bone cancer in dogs. OSA occurs most commonly in large and giant breed dogs such as Rottweilers, Great Danes, Saint Bernards, German Shepherds and Golden Retrievers. The average age of dogs with OSA is 7 years, however dogs as young as 1 year can be affected. The most common location for OSA is in the long bones of the legs, especially near the knee, shoulder and "wrist". Other sites can include the jaw, spine, and ribs. OSA tends to behave very aggressively locally (eating away the bone) and has high rate of metastasis (or spreading) to the lungs. Other less common bone tumors are chondrosarcoma (tumor of cartilage), fibrosarcoma (tumor of fibrous connective tissue), hemangiosarcoma (tumor of blood vessels) and histiocytic sarcoma (tumor of inflammatory cells). The cause of most bone tumors is unknown.

Clinical Signs
Most dogs with bone cancer are taken to their veterinarian due to lameness and/or swelling at the site of the tumor. Sometimes affected bones can fracture (or break) causing severe, sudden lameness. Tumors located in sites other than the legs may become apparent due to local swelling or site dependent signs such as difficulty eating or opening the mouth.

Diagnostic Tests
OSA is usually diagnosed presumptively based on age, breed, history, physical examination findings and radiographic (x-ray) findings. Changes on x-rays generally include proliferation of extra bone and lysis (or eating away) of bone. These findings are very suggestive for OSA, however a definitive diagnosis requires that a sample of tissue be obtained either by fine needle aspiration, needle biopsy, or surgery. These procedures almost always require either heavy sedation or general anesthesia. Often a biopsy is obtained at the time of definitive treatment (amputation). Because OSA has a high rate of metastasis, radiographs (including 3 views) of the thorax are done to make sure there is no evidence of obvious nodules prior to surgery. Baseline blood work including a complete blood count and chemistry profile are done as a preanesthetic workup and to screen for other problems. A thorough physical examination is done to determine whether the patient is a good candidate for amputation.

Treatment
Treatment options for OSA include the following:
1. SURGERY AND CHEMOTHERAPY: Surgical excision of the primary mass is part of an aggressive treatment approach and usually requires amputation of the affected limb. Amputations are done at the level of the shoulder or hip joint. Most dogs recover from amputation surgery well and lead very active lifestyles. Pain management usually includes injectable drugs while in the hospital and oral nonsteroidal anti-inflammatory drugs at home. After a couple of weeks almost all have adjusted to having 3 legs. The estimate for amputation can range from $1200-1800. Dogs that have small tumors located on the distal radius (just above the "wrist") may be candidates for limb-sparing surgery, which involves the removal of part of the radius and replacement with a bone graft from a bone bank. This procedure costs $3000-4000 and has a relatively high rate of complications (primarily infection), but may be a good option in some patients.

Because of the high chance of metastasis, chemotherapy is recommended following surgery. Chemotherapy consists of a combination of 2 drugs, doxorubicin and cisplatin, which are given alternately every 3 weeks for a total of 4-6 treatments. Doxorubicin (trade name is Adriamycin) is given intravenously in the leg over 20-30 minutes and tends to have minimal adverse effects, however gastrointestinal effects, bone marrow suppression and cardiac toxicity can occur. Cisplatin is also given intravenously in conjunction with 6 hours of intravenous fluid therapy in order to protect the kidneys from drug toxicity. The most common adverse effect of cisplatin is vomiting which can usually be managed medically and only lasts about 24 hours. In general, chemotherapy is well tolerated in dogs, and our goal is that they maintain excellent quality of life throughout their treatment. The estimate for a treatment with doxorubicin is $250-350 and with Cisplatin is $500-600. An alternative protocol would include 5 biweekly doses of doxorubicin. Please see the handout on chemotherapy for more details. The average survival of dogs treated with surgery and chemotherapy is 10-12 months. Chemotherapy alone has not been shown to be effective against OSA tumors.

2. PALLIATIVE RADIATION THERAPY: Radiation therapy (RT) can be used to decrease pain associated with OSA tumors and can help slow progression of local disease. "Palliative" therapy is any treatment used to help make a patient more comfortable. The vet school at LSU is the closest facility for RT in dogs. The protocol consists of weekly treatments for 3-4 weeks. General anesthesia is required for dogs undergoing RT, and adverse effects of treatment are generally very minimal to none. RT is beneficial in about 75% of dogs. It does not do anything to slow metastasis and therefore the prognosis with RT alone is 4-6 months. Chemotherapy can be added to RT to hopefully slow metastasis and act as a radio sensitizer, making the cancer cells more sensitive to the radiation. Protocols similar to those mentioned above can be used. The estimate for 4 doses of radiation therapy is approximately $2000.

3. PALLIATIVE MEDICAL MANAGEMENT: Medical management includes drugs used to manage pain. We use nonsteroidal anti-inflammatory drugs (NSAIDS) such as Deramaxx, piroxicam, and Rimadyl. These COX enzyme inhibitors decrease inflammation associated with the tumors and may also have anticancer effects by decreasing the blood supply to the tumor cells. It is important not to give NSAIDS in conjunction with any other anti-inflammatory drugs such as aspirin or steroids. Tramadol is an oral pain medication similar to codeine which can be used in conjunction with NSAIDS. Transdermal opioid patches (Fentanyl patches) can be used to manage pain for 2-3 days at a time.

Prognosis
Dogs treated with surgery and chemotherapy have an average survival of about 10-12 months. Dogs treated with palliative radiation therapy can do well for as long as 6 months. The prognosis for dogs with OSA without treatment, with amputation alone or with medical management alone is 4 months, as most dogs will have metastasis within that time. Dogs that do not undergo amputation or RT, however, are often euthanized within days to weeks due to uncontrollable pain.