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Bone cancer in dogs and cats: diagnosis and treatment

Osteosarcoma, or bone cancer, is a scary disease. Even the name sounds scary. How does bone cancer differ in dogs and cats compared to people? Does bone cancer act differently between dogs and cats? These are all good questions.

After some research on human osteosarcoma, I found that this cancer carries a much better prognosis than it does in our canine counterparts. If the cancer is caught before metastasis (spreading to other organ systems either through the bloodstream or the lymph ducts) and treated aggressively, it carries a much better long-term prognosis.

Osteosarcoma is the most common type of bone cancer in dogs, making up approximately 80 percent of all bone tumors. Osteosarcoma is more common in larger breed dogs. Those breeds with a higher risk include Saint Bernard, Great Dane, Irish Setter, Doberman Pinscher, German Shepherd and Rottweiler. Mixed breed dogs that are of these types are also at risk.

Osteosarcoma is most common in dogs over seven years of age. The first signs can be somewhat nebulous because the dog will have a lameness that just does not resolve. As the cancer progresses, then swelling will develop on the affected limb. When I was in school one of my professors had a good rule of thumb when describing the most common sites: "toward the knee and away from the elbow," he would say.

Unfortunately, osteosarcoma in dogs is also very aggressive. Not only does the cancer destroy the bone around it, it is also estimated that approximately 90 percent of dogs have metastasis at the time of diagnosis. Treatment involves complete removal of the tumor via complete amputation or limb-sparing techniques. Limb-sparing techniques involve removal of the tumor and then stabilizing the area with pins and rods until new, healthy bone can fill in or a prosthesis is placed.

Most dogs are able to ambulate well on three legs and, unless there is significant arthritis in other limbs, amputation is the surgical treatment of choice for most owners. Amputation alone only carries a survival time of approximately four to six months after surgery. Surgery and chemotherapy increases survival time to between eight months and 1.2 years.

Cats do not develop bone cancer very often (4.9 cats per 100,000). The signs are similar to dogs in that the cat will start favoring the affected leg and swelling will develop. Osteosarcoma in cats is locally invasive (the tumor destroys the normal bone around it) but it does not tend to metastasize very often. Therefore, amputation of the affected limb is usually curative (if there is no evidence of metastasis at the time of diagnosis).

The key to treatment with this tumor is early detection, so make sure to have any limping or lameness evaluated quickly by your veterinarian.

Dr. Kearns has been in practice for 14 years.

Author: 
Matthew Kearns, DVM