Osteosarcoma: Bone Cancer in Dogs

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Bone cancer can strike any dog at any age. The most common form of bone cancer in dogs is osteosarcoma, which is highly malignant and aggressive. It occurs in large breed dogs more often than small breeds. Osteosarcoma can grow in any bone, but the leg bones are the most frequently affected.

Signs of Osteosarcoma in Dogs

When a dog is suffering from osteosarcoma, you may see some or all of the following signs:

• Lameness which gets progressively worse over time.
• Swelling of the leg in the affected area.
• Decreased appetite due to pain.

As more tumor cells replace normal bone cells, the bone becomes more prone to fracturing. These are called pathologic fractures, and they do not heal because there is no healthy bone at the fracture site.

Diagnosis of Canine Osteosarcoma

Your veterinarian might suspect osteosarcoma when you take your dog in for limping and he or she feels the leg. The doctor will note that the area is quite painful for the dog and might be able to feel a firm swelling.

X-rays of osteosarcoma lesions have a characteristic look of decreased density due to the loss of normal bone. Most of the time, the veterinarian can comfortably diagnose a bone tumor based on the history, physical exam, and x-ray findings. However, definitive diagnosis can only be made through evaluation of a biopsy or fine needle aspirate sample.

After diagnosis, the rest of the dog's health is assessed through blood tests, urinalysis, and further x-rays to determine whether there has been metastasis, or spread, of the cancer.

Treatment of Osteosarcoma in Dogs

Dogs with osteosarcoma must be treated for pain. When the cancer lesion is in a limb, amputation is the best way to remove the pain. Most dogs do incredibly well getting around and adjusting after amputation surgery. Chemotherapy can follow amputation or cases in which limb-sparing surgery is done to remove as much tumor as possible without amputation.

It's important to understand that, even with amputation surgery, dogs with osteosarcoma have an average lifespan of 3-5 months. Even if obvious cancer isn't found elsewhere at the time of the bone tumor diagnosis, cells have traveled and seeded other areas of the body.

Radiation therapy can sometimes be done instead of amputation. In about 75% of cases, dogs improve for between 2 and 4 months with this treatment, but they are at higher risk of developing a pathologic fracture in the area of the tumor because they are using the limb more.

Pain medications are necessary for dogs before, during, and after amputation surgery or if they do not have such surgery performed. Your veterinarian is best suited to determine the type and dosage of pain medications that will best benefit and be safest for your dog.

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