What is a canine osteosarcoma?
Osteosarcoma is the most common primary bone tumor in dogs, accounting for roughly 85% of tumors in the canine skeleton. They can be quite painful and can appear in any bone, although they are most frequent in front limbs and long bones, including the radius, ulna, humerus, femur, and tibia. Osteosarcomas appear to affect middle-aged to older large to giant breed dogs more commonly. The cause of this tumor is largely unknown.
What are some of the signs of osteosarcoma?
Lameness is the most common sign of osteosarcoma in dogs. Lameness may develop suddenly (after vigorous activity, for example) or slowly. Depending on the location of the tumor, a swelling or mass-like effect may be seen in the affected leg. Any lameness in a large-breed dog that does not promptly resolve with symptomatic therapy should be examined by a veterinarian.
Osteosarcoma is both a locally invasive tumor and a tumor with a high likelihood of metastasis, or spread, to other organs, most commonly the lung. Approximately 90-95% of dogs with osteosarcoma are considered to have metastasis at the time of their diagnosis, although metastasis will only be evident at the time of diagnosis in approximately 10% of dogs and in others the metastatic tumors are considered to be microscopic.
How is osteosarcoma diagnosed?
Radiographs, or X-rays, of the affected leg and the thorax are commonly used to determine the stage or extent of the cancer. Dogs with enlarged lymph nodes will also typically have the lymph nodes sampled for microscopic examination. Radiographs of affected legs are often highly suggestive of the diagnosis, and biopsies are not necessary for all dogs with compatible lesions on radiographs. Often, obtaining blood for a complete blood count and biochemical profile, and a urinalysis will be advised, as these can help assess overall health and provide information that potentially influences treatment recommendations. When aggressive therapy is being considered, a computed tomography, or CT, examination of the lungs will also be recommended to screen more precisely for metastasis.
How is osteosarcoma treated?
Amputation to remove the primary tumor, combined with chemotherapy to treat the metastatic disease, is the best treatment for preservation of quality (relief of pain) and quantity of life for dogs with the limb form of osteosarcoma.
Not every dog is a candidate for amputation and the decision to amputate is often difficult for owners. Dogs with severe arthritis in the unaffected limbs or weakness due to neurologic disease may not be candidates for amputation. Dogs can function on three legs much better than most owners think. Some institutions offer limb-sparing surgery, in conjunction with chemotherapy, but this can only be done when the tumor is in the radius or ulna near the carpal joint (wrist). Generally, chemotherapy treatment includes 5 doses completed over 3-4 weeks. Drugs commonly used include cisplaitn, carboplatin and doxorubicin. Amputation without chemotherapy can remove the source of pain but, generally, metastases will become apparent in 3-4 months.
Palliative therapies are those aimed at keeping the leg more comfortable so the dog can live with it longer. Radiation therapy will improve comfort in approximately 70-80% of treated dogs. Generally, only a few large doses of radiation are administered. Administration of analgesics, which can be done in conjunction with palliative radiation therapy, can improve the level of comfort in some dogs.
Additionally, a class of drugs known as bis-phosphonates is being tried for dogs with osteosarcomas. These drugs inhibit bone resorption or break down. They have been used in the human field for osteoporosis and in the treatment of tumors that have metastasized to bone to relieve pain.
Dogs with osteosarcoma in other bone locations are often treated with a combination of surgery, radiation therapy, and chemotherapy.
What is the prognosis for dogs with osteosarcoma?
The prognosis for dogs undergoing surgery to remove the primary limb tumor (amputation or limb-sparing surgery) and treated with chemotherapy is fair to good. About half of dogs with osteosarcoma treated in this manner will be alive 1 year after diagnosis; approximately 25% of dogs treated in this fashion are alive 2 years after diagnosis, and occasional dogs will be cured. Dogs treated with either amputation or palliative radiation therapy live, on average, approximately 6 months before complication of the local tumor or metastatic disease cause death or prompt euthanasia.
Where can I get help if my dog has osteosarcoma?
Cancer of any kind is a diagnosis no pet owner wants to hear, but our board-certified veterinary oncologists can help you get an accurate diagnosis and develop a treatment plan. Call 509-335-0711 to schedule an appointment or visit our oncology webpage for more information.
This information is not meant to be a substitute for veterinary care. Always follow the instructions provided by your veterinarian. Washington State University assumes no liability for injury to you or your pet incurred by following these descriptions or procedures.