Osteosarcoma in Dogs

Overview of Canine Osteosarcoma

Osteosarcoma is a type of cancer that typically arises in the bones of the limbs, or the appendicular skeleton. Less commonly, it may occur in the bones of the spine, pelvis, and skull – the axial skeleton. Osteosarcoma is the most common type of bone cancer, and it is estimated to occur in more than 8,000 dogs in the United States each year. Osteosarcoma occurs very rarely in cats.

The cause of osteosarcoma is largely unknown. It is most common in large-breed dogs (over 50 pounds), so its development in some animals may be related to rapid early growth with resultant increased weight and forces being placed on the bones. It has occurred at fracture sites where metal plates or pins were used to repair the bone, suggesting that chronic irritation may be associated with development of this type of cancer. Rarely, it can occur in areas that have been exposed to radiation therapy.

Male animals are affected at the same rate as female animals. Most dogs are 6 years of age or older when they develop this tumor; however, it does occur in animals as young as two years of age.

This is a highly metastatic, meaning it spreads to other parts of the body, and life-threatening form of cancer and usually causes lameness and general debilitation of your pet during its development and progression. Average life expectancy in dogs that receive treatment in the form of amputation, or surgical removal of the leg, and chemotherapy is 10 to 12 months. Without treatment, life expectancy is usually two to four months. When this cancer affects the axial skeleton, the prognosis is usually worse but is dependent on the site and on the type of surgery and follow-up care. Some animals with tumors of the lower jaw can do well for a year with only surgery.

What to Watch For

Signs of Osteosarcoma in Dogs may include:

Diagnosis of Osteosarcoma in Dogs

Diagnostic tests are needed to recognize osteosarcoma and exclude other diseases that may cause similar symptoms. Tests may include the following:

Treatment of Osteosarcoma in Dogs

In addition to administration of pain medications, treatment for osteosarcoma may include the following:

Home Care and Prevention

Your veterinarian can prescribe pain medications to make your dog more comfortable. You may be asked to administer pain medications to your dog until definitive therapy can be done, but do not give your dog any pills that have not been prescribed or recommended by a veterinarian. At the time of surgery a narcotic pain patch may be placed on the skin. These patches release a constant level of pain medication that is absorbed through the skin.

You should limit your pet’s activity to prevent further pain and to reduce the likelihood of a pathologic fracture, which is an abnormal breaking of the bone due to the cancer weakening it, prior to definitive therapy. Your dog should not run, jump or play during this time and you should watch him carefully or give him assistance when he is climbing stairs or getting in and out of a car.

There is little that you can do to prevent bone cancer from occurring in your pet because the cause is poorly understood. Have your veterinarian evaluate your pet for any lameness that develops. Most forms of lameness are likely to be associated with arthritis or injury to ligaments and tendons. If your dog is not getting better with rest and anti-inflammatory drugs, radiographs of the affected region should be taken to exclude the presence of a bone cancer as a cause of lameness.

In-depth Information on Osteosarcoma in Dogs

Lameness is a general term used to describe pain or discomfort experienced when your dog moves normally or exercises minimally. Although your dog may develop lameness due to arthritis, ligament or tendon tears, or cartilage injury, lameness is also a cardinal sign of osteosarcoma. Therefore, any unexplained or chronic lameness in your pet warrants further investigation.

Some tumors arise from tissues associated with bone and can mimic osteosarcoma. These include:

These tumors are far less common than osteosarcoma and tend to affect the axial skeleton (skull, ribs and spine) more often than osteosarcoma.

Other causes of lameness that must be considered and potentially differentiated from bone tumors include:

Veterinary care should include diagnostic tests and subsequent treatment recommendations.

In-depth Information on Diagnosis

Medical tests are needed to establish the diagnosis of osteosarcoma, exclude other diseases that may cause similar symptoms, and determine the impact of osteosarcoma on your dog. Tests that your veterinarian may wish to perform include:

Your veterinarian may recommend additional diagnostic tests to ensure optimal medical care. These are selected on a case-by-case basis. An example includes:

In-depth Information on Treatment

Treatments for osteosarcoma may include the following:

Every oncologist has a preference and may pick certain drugs or combinations based on your pet’s general health and the appearance of the tumor. All of these treatments have about the same impact on prolonging survival, an average of about 10 to 12 months from diagnosis. Common side effects include a decrease in your pet’s white blood cell count approximately seven to ten days after each treatment, nausea, vomiting and/or diarrhea. Each of these drugs also has unique side effects, which your oncologist will discuss with you, depending on the drug chosen for your pet.